Sheldon Browns archive has a lot of info for keeping bikes on the road.

I've picked up some 8 speed cassettes to harvest cogs from so I can have a 13-30 7 speed "century' special. I'm pretty comfortable friction shifting with 7 speeds, so its ok if the indexing isn't perfect.

I've seen some references about running "8 of 9 on 7" which would be a way to transfer an entire 9 speed group over to an 126mm 7 speed bike and use 9 speed indexing -1.

In general, I think I've stocked enough 7 speed consumables up to make it the next 25 years. At that point I'll probably give in and get a Velomobile with a cold fusion warp drive pedal assist.