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

There's really no advantage to 2.5" tailpipe, and arguably a disadvantage.
EXCEPT.
There is an advantage to 2.5 mufflers and the first turn after the muffler can be tight.
So the trick is where to drop the diameter after the muffler.
You didn't say how high rpm this swap will be spinning but I'm assuming you may take this to the track.

Pics of the Accurate tailpipes we reused with the new system. Maybe I'll fix it this year.
https://www.forabodiesonly.com/mopar/threads/2-5-exhaust-vs-2-25-or-even-2.435185/post-1972511421Backstory.
Atmospheric pressure at the tailpipe is 14.7 psi against the pressure flowing out. The further up the system that 14.7 psi gets, the more it will slow down the flow out the exhaust ports of the engine. Keeping the velocity up near the exhaust ports will reduce reversion on any engine, but especially an engine that spends more time at low to mid rpm, or has to spin through low to get to high rpm.

Stepping up through the primary tubes is usually a good technique to keep the velocity up and yet not restrict higher rpm flow. Pipe-max shows H- Pipe or any other major change should be about 20" after the primary tubes join for most of our engines. By the time the exhaust is at the mufflers its cooling and the mufflers cool it much more. Mass of the exhaust gas stays the same but the volume is less.