What is the biblical basis for elder disqualification? The Bible speaks to the qualifications of overseers and deacons, and also mentions that they are to be held to a higher standard than the rest of the congregation.

What Biblical basis exists, then, for the disqualification of those who are called to shepherd? Specifically, how to these align with the Biblical doctrines of repentance and forgiveness (if, say, a leader was repentant and sought forgiveness over a sin)?
I think that you are confused about the purpose of the deacon or bishop ordination. They are not ordained for their own benefit, but for the benefit of all the church. Therefore it is important that they are not a reason for scandal and offence.

The fact that someone isn't found fit to be ordained as deacon, presbyter or bishop doesn't mean that he can't repent, is unforgiven etc.