Does anyone have a good source for a 2.25" exhaust flange? Hopefully something thicker than stock.

Most muffler shops should have the flanges, most likely for each size pipe....at least the shop I used did. They did my exhaust with 2 1/4" pipe using thick universal (elongated bolt holes) flanges. He was going to insert one of those donut inserts into the manifold outlet instead so the pipe could be flared and be sealed even better, but being I honed out mine not exactly to the 2 1/4" dimensions needed for one, I had to stay with the stock type setup. I'd check some shops, I'll bet they have them.

The shop that did my exhaust did the exact same thing as LWS1967.