Calculation of national rating In order to calculate effect on national rating, should it be enough to choose the relevant k coefficient (assuming this is what makes for the discrepancy between national rating and FIDE rating) and plug it in here: https://ratings.fide.com/calculator_rtd.phtml ?

Furthermore, is there a resource out there to find k coeffients per country (I'm located in Israel, so if anyone knows that specifically, even better).
In order to calculate effect on national rating, should it be enough
  to choose the relevant k koefficient (assuming this is what makes for
  the discrepancy between national rating and FIDE rating) and plug it
  in here: https://ratings.fide.com/calculator_rtd.phtml ?


No. For the simple reason that countries use different methods for their rating/grading system. Some use an elo system others don't. England, for instance, uses a completely different system.

If you go to the ECF grading website and click on help, on the left hand side of the page, then towards the bottom of the help there is a section describing how the ECF calculate their grades. 


  HOW ECF GRADES ARE CALCULATED
  The basic method of calculation is as described in the next few paragraphs. For juniors, however,
  there are differences as described further down.
  
  Points are allocated in respect of each game. For a win you score the
  opponent's grade plus 50, for a draw the opponent's grade, and for a
  loss the opponent's grade minus 50. "Grade" means his grade current at
  the time of grading. There is a proviso that if your opponent's grade
  differs from yours by more than 40 points it is assumed to be exactly
  40 above (or below) yours. This applies whatever the result.
  
  If an opponent (or the player himself) is ungraded, a "starting grade"
  is estimated, using all available information. See Estimating a
  starting grade for an ungraded player below. Note that FIDE ratings
  are ignored. An opponent who has only a FIDE rating will be treated as
  ungraded.
  
  In the interval between the end of a grading period and publication of
  the new grades, the "current" grade for calculation purposes is the
  new, as yet unpublished, grade.
  
  The grade is calculated by dividing the total number of points scored
  by the number of games played. If there are 30 or more games in the
  most recent 12 months, then the grade is based on these games alone.
  If there are not, it is based on the most recent ** 30 games played;
  or on all the games played in the last 36 months if that is less. In
  no case does calculation go back more than 36 months. Where games are
  brought forward from a previous period, they are not recalculated. The
  number of points scored for a game always remains the same.
  
  ** "Most recent" has a special meaning here. In principle the program counts backwards till it reaches 30 games. But there are certain
  disadvantages (see Appendix) to applying this naïvely. Instead, if the
  30th game falls part way through a 6-month period, the program will
  take as many games from that period as it requires in order to make up
  the 30; but they will be notional games calculated at the average
  score for the whole 6-month period.
  
  How is "most recent 30" interpreted if a game has been reported late
  and graded in the "wrong" period? Answer: the game will be listed
  under the grading period in which it was reported and calculated, and
  it will go into that period's grade with a notional playing date of
  1st January (or 1st July as the case may be). This notional date will
  be used, where necessary, to determine the game's position in the
  backward count to 30.
  
  Rounding
  Grades are calculated to the nearest whole number (halves
  go up). Rounding is done once, at the end. A grade, once rounded and
  published as a whole number, is henceforth deemed to be that whole
  number.


You say -


  I'm located in Israel, so if anyone knows that specifically, even
  better


Really? Do you play chess in Israel? Do you have an Israeli rating? Can you read Hebrew? 

I'm guessing some of the answers must be "No" since otherwise you would be better placed than 99.9% of forum members to find out the information for yourself and are only asking out of sheer laziness.

My ICF rating is in the 1800's and my k factor is 12.

Boris Gelfand's ICF k factor is 10 as you can see from the calculations for his Israeli rating from his games played abroad (i.e. converting his opponents' FIDE ratings to ICF and then using them to calculate changes to Gelfand's Israeli rating). This link takes you to Gelfand's ICF rating page and then you will have to click on  משחקים בחו"ל (middle / fourth of the box links underneath his main details).

Here is the same page for Liel Levitan, the European Schools girls U7 champion. Her Israeli rating is 1445 and her k factor is 14. Again, on the page click on משחקים בחו"ל to get to the calculation page.

Here is the Israeli rating list (but I don't understand why you couldn't get this for yourself if you are living and playing in Israel?) You can find players of different strengths and ages and check their k factors. I know the ICF website is hard to navigate. I found the old one from about 5 years ago much easier. It used to give the calculations, including k factor, for every game, not just the foreign ones, so including the Israeli ones.

As you can see from the FIDE Ratings Change Calculator you cannot type in any k factor. That means that in general you cannot use this for ICF ratings and for other federations only if they use the same k factors.