2.5x2.5 should not be that hard to find. And Receiver tubing isn't the same either- the interior weld seam has been removed and its got a slightly larger than 2" ID to fit 2" OD tubing easily, and it is usually quite a bit more expensive (but works the same if that's what you happen to have).

If you happen to be near Sacramento, S&K Steel is a great place to buy small chunks of whatever you want, but it doesn't sound like you're in the area...

'97 4Runner, '06 F350, '86 4Runner, '05 WR450
http://home.4x4wire.com/erik