engine

Is the 2011 cts 3.0 the only other engine that’s a direct fit into a 2010 cts 3.0? Also are there any legitimate sites to buy a used engine on?? All I see are scams and car.part has nothing

Few questions.. What other year Cadillac engine will fit directly into a 2010 cts 3.0l RWD(auto)? And are there any good sites and/or forums that are legitimate to buy a used engine from? Craigslist and car-part is a no go, I can’t find anything.