Welcome aboard.
It would help if we knew what vintage drive you are talking about. the old stringer drive and electric shift drives can grenade a section and not take out the other section. however the newer drives will share debris
I would suggest looking in the yellow pages for OMC service centers (may not exist anymore)
additionally, there are many parts for OMC, Volvo and Mercruiser on the Seattle Craigslist. (I have found a fair amount parts and had them shipped to Florida)