Wondering if anyone knows if it is even possible to buy copper pipe
that is 2.5 inches in diameter in 20g & 28g? Or am I just wishfully
thinking? 
I have already checked with some local plumbing &
roofing companies.
Trish
Trish,
You should get 2 1/2" copper pipe at a decent plumbing supplier - but
not the local Home Depot. If you can’t, try a model engineering
supplier or a heating/refrigeration company. Here’s a UK link…
Best wishes,
Ian
Ian W. Wright
Sheffield UK
Look up “copper tube” on the Alaskan Copper and Brass Co. web site,
they have it up to 5 or 6 inches!
Dr. Mac
Yes, Alaskan Copper here in Seattle is a great resource for nearly
anything copper (or metal for that matter). They are a GREAT
resource.
Laney
I thought I didn’t know, and then remembered this place I found some
years ago:
http://www.plumbingproducts.com/athrud.html
Pretty much the whole galaxy full of plumbing stuff of all kinds,
for any interested in that, too…