Got mine at Home Depot, 48" and 60", without the "T". Actually made in the USA, Lowe's had china made stuff.....
To determine straightness or lack thereof, I take two of the straight edges and lay them flat, edge-to-edge, and then turn them over and check the other two edges, again edge-to-edge. If the edges are not straight there will be a gap between them, also use the MK I Eyeball test---more precise than you might think.
Cheers,
Jim