Electronix.com has a ton of Cd pickups. Sega cd 1 + 2, X-eye, Saturn are some of the systems ive been able to fix thanks to them.
Sega Cd 1 -Optima 5s
X eye / wondermega -Optima 6s
early saturns with oval buttons -Optima 6s.
im sure they have a pickup for more consoles than that ive just never had to fix anything else.
the 6s pickups are very reasonable, around 15 bucks.
their shipping is fast too.