*I agree with DD.. Most muffler shops should be able to do it, though they may have a problem with the SIZE or the pipe..
you can also get a flex pipe for temp use but Id not trust that long time.
Side note: you know those blasted new fire rings that consist of concentric culvert pipe sections with concrete in between.. No way can you get one up to let air into the fir pit (Well you can tunnel under)
I had a muffler shop bend a piece of tail pipe 90 degree bend a few inches (As close to end of pipe as they could make it) 90 degrees the other way about 4-6 inches (roughly the height of the rings) from that, then another roughly the width (bit wider) of the concrete ring from that (same direction so pipe now heads down) and another not quite as far down (Remains just above the ground)
I mounted a small whisper fan (like a computer fan but smaller) in the "outside" end of the pipe, 12 volt rechargable battery powers fan.
Home is where I park it!