If they are Thin lite fixtures you can replace the ballasts easily.
you can find them here
http://store.solar-electric.com/12vodcbaforf.html (http://store.solar-electric.com/12vodcbaforf.html)
Barry,
Thanks for the recommendation. I ordered the IOTA ballast for the BIAX 4-pin lamp in the kitchen area. I "smoke tested" it today, and the lamp worked immediately. The ballast is relatively large, and will not fit inside the aluminum housing of the fixture that is mounted inside a larger recessed wooden housing in the ceiling. I will need to pull the fixture in order to drill holes in the side of the aluminum housing. I plan mount the ballast there with screws so it will be secure and thermally coupled to the aluminum housing. The housing will provide a heat sink for the ballast.