These Minolta flashguns will be FULLY compatible with your a200.

PROGRAM FLASH 5600HS(D)

PROGRAM FLASH 3600HS(D)

PROGRAM FLASH 2500(D)

Of course all the current Sony flashguns will be FULLY compatible.

FLASH HVL-F36AM

FLASH HVL-F42AM

MACRO TWIN FLASH KIT HVL-MT24AM
FLASH HVL-F56AM

Ring Light HVL-RLAM

I once had a Sunpak but was not impressed. I've never had a Metz 36AF-3 ... but at the price and with their reputation it should be compatible.

On balance I would try to get good second-hand example of one the Minolta flashguns. I have a Minolta 5600HS(D)and it is extremely good with both my a700 and a350.