Here's some sources for aluminum tubing: TW Metals, 303-340-1050,
Marmon Keystone, 303-296-7473 (Marmon Keystone has warehouses in Houston
and Kansas City), and Ryerson has many locations throughout the U.S.A.
Ryerson in Dallas is 214-637-4710, in Houston 713-675-6111, in Kansas
City 816-471-3500, in Omaha 402-895-5056, in Tulsa 918-428-3841, St.
Louis 314-231-1020, or Ryerson in Denver is 303-287-0101. Ryerson's
catalog shows drawn 6061-T6 and 6063-T832 round tubing from 3/16"
diameter with a .035" wall all the way up to 1 7/8" diameter with a
.058" thick wall. Stock lengths are 12 feet. Unfortunately, in the
metal supply industry, what the catalog says is most often a far cry
from what they actually have in stock. The industry is pretty good with
packaging for safe shipment. You'll probably be shipping any tubing
purchased from the above sources. Why not call an antenna manufacturer,
Mosley in St. Louis, for example, to determine who they buy their tubing
from? That would locate the best source for variety of telescoping
sizes and a source with available stock from a supplier already tuned
into antenna requirements. Mosley probably uses Ryerson out of
Ryerson's St. Louis office. I'll bet this route won't be cheap. Why
not make 2 or 3 antennas and get a buddy or two to help share the costs?