Hi welcome to the forum. I probably won't be the only one to say (parrot fashion): Tohatsu 9.8 2 stroke, Tohatsu 9.8 2 stroke, Tohatsu 9.8 2 stroke, Tohatsu 9.8 2 stroke, Tohatsu 9.8 2 stroke...
Check a search for more but for a huge number of people this is the often recommended circa 3m SIB engine. Why? Reliable, very light, super simple to service, great pick up, quiet, burns virtually no fuel, etc, etc.
As for where to buy, eBay is probably the best bet to find one at a good price (second to buying from a fellow RIBnet member) but you really want to (must) see an engine started and running before you buy it. Buyer beware as always.