T&S Tubing & Shafting Inc
2266 Nicholson St S, Prince George, BC V2N 1V8
250-563-3343
There may be others, but these are the only guys I've purchased from.
They may have crops (pre-cut leftovers) at an okay price, but don't buy a small chunk cut off a big piece; that's way more expensive.
I have bought tubing there for my hardtails and other frame modifications. The cheapest is to buy 20'. They will cut it in half at no cost so you can haul it.
The have d.o.m. in various wall thicknesses.
Peace & Grease, Dennis