Or is he available for hire by Marvel/DC, etc.? Does he do commissions?

He has been doing a lot of writing in the past year in Robin Snyder's The Comics, but I don't think any artowrk has been published in about 2 years.

As far as commisions go, I think he's been asked and has turned everyone down. For Ditko, I suspect the money doesn't entice him, he just doesn't find it interesting to go over old territory. Herb Trimpe, who was doing commision work for a while, emailed anyone on his internet list that he will no longer be doing fan commisions. He was getting bored drawing the same characters over and over. I think its understandable.