Cassettes and freewheels are still out there, new, if you look.

Shifters are a little tougher, but I just saw some some downtube type on evil bay the other day as BIN right at $30.00. Not free, but not horrible either.

One of the neat things about 7-speed is the cog spacing is the same 5.0mm for both cassettes and freewheels. You can use a 4mm spacer, on the inside of the cassette, if you want to run one on a modern 8,9, 10-speed Shimano splined hub.

And, if you really want to get your freak on, I notice Campy 8-speed cassette is also 5.0mm spacing, so it should work just fine in a Shimano 7-speed setup, although, you will only be able to shift 7 gears. I mention this as Campy 8 was somewhat of a short lived oddball. Might be able to pick up a nice wheel cheap.