Yes. I assume this is to replace a Yanmar/Kanzaki transmission. What gear ratio? There are 2 ratios, 2.1 and 2.63. (if I remember correctly).
Last August I had to replace the transmission on my 3JH2e and could only find 1 in the country. Mack Boring the east coast distributor said they might be able to get one in 4 to 6 weeks and it would have to be manufactured as there was no inventory for the 2.63 ratio.
The one I found was at Fred Warren (?) on eBay. They are an west coast distributor that only sells on eBay. I bought it.
In addition to the transmission, you will need a new mounting plate, damper, flange, and longer bolts.
Probably. When I checked out Fred Warner with a trusted transmission guy he said Fred Warner was a division of some other brick and mortar marine business and could be trusted. I don't recall which business it was, but it was large and well know on the left coast.