Flanges/Gaskets for OEM exhaust

[CanuckQx4]

My exhaust on my car is old and rusted. I just passed emissions tests with the factory cat, so now I think I want to remove the factory cats and check there condition and possibly even replace/delete them AND then build an entire new exhaust all the way to the back

If I wanted to build a new exhaust in my garage I will need the correct flanges if I want to make new pieces.

I know a guy that can make flanges for you if you send him the gasket, he can make that into 3/8" thick steel or whatever.

I cant seem to find the part numbers for a gasket or weld on flange.

Since I wont be sure if I want to make my exhaust start from the bottom of the factory exhaust manifold or keep the factory cats and make my exhaust start from the bottom of them. I would need both gaskets or flanges if they sell them

Has anyone bought flanges for our trucks with success anywhere??

Thanks for any help