gas boiler exhaust vent?

I have a gas boiler in the basement that's vented through the joist just above the foundation. The pipe basically rises 5' from the boiler, makes a 90, and goes 3' to the outside. It's 3" class A (I think?) pipe, with a flange and cap outside. Over the summer I replaced some rotten siding and plywood, and found the boiler exhaust was rusted as well.

I'm having a tough time finding someone who sells this stuff online. The part I really need is the flange/cap that's mounted on the outside wall, but can't seem to locate one. Can anyone point me in a direction? Thanks

Thanks. I found a Tjerland cap on Grainger, About $145 with shipping.