A1 type triangular style? All that's out there right now are Colt made GI surplus pieces, so hit the parts houses.
A2 type round? Again, I'd hit the surplus parts sellers. I've found GI surp pieces at competitive prices at shows.
Carbine type round HGs seem to be the area where the most junk is floating around. My own experience is that the Colt M4 type are the stiffest and most rugged. Rock River has an M4 set that I swear is the Colt unit, but about $5 cheaper.
In the full round old style carbine HGs, I have not seen anything that comppares to what Colt put on their early carbines. That Bushmaster unit I got was total trash, though I haven't seen their new style oval M4 type.
My own attitude is that you're best off getting to a gun show, and hitting the parts guys tables til you find what you want.