Pete,
Around here (granted I am in the car capital of the world) there is a considerable number of automotive restorers, automotive upholstery shops, etc. I would suggest that any automotive upholstery shop should be able to repair the seat by replacing one, more or all of the springs. This is as about rudimentary as repair gets. I just did a quick search on Yahoo! Yellow Pages, and there are 12 automotive uphosterers in Seattle alone; 78 if you go out to a 50 mile radius. Go to Yahoo yellow pages, type in Seattle as your location, and automotive upholstery. Once you get the results, start manning the phones, my guess is you won't have to travel far.
Let me know how it works out!
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored