The on-line parts websites are a great resource even if you just need to know a part number (and don't intend to order from them).
I looked at cyclepartsnation.com, and found this for the 1985 200M:
BATTERY ASSY. (YB14A-A2) (YUASA)
Still available from Honda for $55.01 .
The prices vary quite a bit from website to website, and if you go to the parts counter at a Honda dealer the cost will definitely be more than that.
However, if you go to a generic battery dealer and ask for a suitable replacement for a "Yuasa YB14A-A2" they should be able to hook you up.
- Frank
1984 200ES Big Red
1985 350X (x2)
1986 350X
1986 250SX
1984 Auto-X
1984 ATC70
1985 ATC70