Camping World Catalogand another
Camping world linkAnd one last linkSearch took me less than 2 minutes. A bit longer to copy paste and type.
All links are to camping world but if you go to any major RV dealer they will likely have at least one of the products listed,,, NOTE these are short "Dogbone" length adapters you will need a 12 ga EXTENSION cord from Sears or K=mart (Best) or one of the home improvement stores (The Sears/Kmart brand has a lock-on outlet I like rather well) to feed it.
You can also get 50-15 amp RV plug (Blade not twist lock) type from the same sources, just back up a page on CW's web site (Click on Electrical Adapters near the top of the page) and likewise at most RV stores, both puck type and dogbone type.