Hi Sir,
Fleabay is a good place to find both watches or the SCWF forum. Vintage 600metres usually go for around £400-500 on fleabay, some can reach £700 or more. Both are cracking watches biggest pain with 600m is wrist roll, watch likes to roll around the wrist I've owned 2-3 600m, and about 2 Seiko 1000m TiN versions.
Regs
Bry