WHere to buy 321 stainless steel?
 

I was just curious on where to buy 321 stainless steel bigger than 16 gauge. I've looked online and only was able to find 16 gauge. I know its expensive. I just wanted to price out the cost on material for a custom manifold. Looking for 1/2" plate for flanges, and sch 10, sch 40, or an 11 gauge or thicker piping

Looks like mcmaster only goes up to 1/4":
McMaster-Carr

Amazon has some, but it looks like it's only 4" wide... more like bar stock than sheet imo:

for the tubing your best bet is probably burns stainless:
Burns Stainless LLC - 321 SS Tubing

They'll probably be able to tell you where to get plates for the flanges.

First, due to the thickness there is no advantage of using T321 for a 1/2" thick flange. T304 is more than adequate there, just be sure to use the correct welding rod to join it and T321. Second, the strength of T321 at high temp is so superior to T304 that the whole point of using is to avoid heavy wall fittings. I certainly wouldn't use anything heavier than Sch 10. Frankly I'd be comfortable with 16 Ga if double-slip fitting connections are used. Constraining everything with welds jumps the thermal stress loads significantly.

Sch pipe fittings should be available from industrial piping suppliers.

I found a few places but I need to e mail them for a price. I'm just curious right now, I don't want to bug them for a price until I really need it.

You think 16 gauge 321 stainless is good enough for a turbo application?