Just do a search for Fulham workhorse ballasts online and you will find places that sell them. I think champion lighting sells them but I believe there are sites that sell them cheaper.
I think I bought a workhorse 7 to run 4 bulbs and a workhorse 5 to run 2 bulbs. Don't quote me on that because its been a few years since I last replaced the ballasts in my tek light.
I never replaced my sockets. The only thing i could suggest is that if you plan to keep this light for a long time I would suggest mounting the ballast outside of the fixture if possible. That way if a ballast ever needs to be replaced again you will not have to take apart the entire fixture.