Where to get pre bent exhaust pipes and any suggestions on how to swage them to fit over mufflers?

Usually the muffler inlet/outlet slips over the pipes going in/out. They also make a ton of different adapters for making various exhaust pipe joints. I've used these with success too:

Summit Racing SUM-681250 Summit Racing™ Lap Joint Band Clamps | Summit Racing

They make them for butt connections too:

Summit Racing SUM-683250 Summit Racing™ Butt-Joint Band Clamps | Summit Racing