Alternative for Technic, Gear Rack 1 x 7 with Axle and Pin Holes? We are trying to build a MOC which requires Technic, Gear Rack 1 x 7 with Axle and Pin Holes and we don't have that. Could we build it? Or are there any alternatives?  

FYI we do have Technic Gear Rack 1 x 4 and 6630 - Technic, Gear Rack 1 x 8 with Holes
If it's your own creation, you should be able to adapt your model to fit the rack you have. One tricky problem I can see is if your construction is built as most studless models are nowadays and features uneven dimensions - which means a 7 rack is indeed easier than a 8.

You can of course build something around the old 1x4 rack place but it might get awkward depending how you want your model to work. Something like this might already work fine:



Also, I wouldn't discount the worm screw, as it can work as a rack as well:



Of course, this is just an example; with this solution you have a lot of freedom as to what you will connect at the ends of the axle, as well as to the length of it. Again, depending on your model, you'll surely be able to find something that suits your needs.