Difficult to find at a "reasonable" price, sadly. I have two dead ones over at AmigaKit right now. They can't fix either of them so I'm working on getting it off to someone else for a try.
Stan on AmiBay repairs and upgrades them. Might want to drop him a line. I've got 3 boards he worked on and the work is great. His prices are ok but the cost of shipping there and back are high but not his fault.