Don,
If you're looking for a one-off, eFunda is the place.
Properties for your cross section are
here.
Material properties are
here and
here.
Finally, the calculator for a simply supported beam is
here.
I think you'd plug in a load until you exceeded the yield strength by a good bit. Problem being, you're specifically trying to yield it and that gets into the non-linear range of things that aren't as pretty.
The actual equations to figure the same thing aren't very bad, but it's 1am and I don't know if I'd need to cover everything from torques and moments up to the bending beam stuff or if I could skip ahead a few chapters.
Incidentally, first run the equation thing until you hit yield, then run it until you hit the ultimate tensile strength. UTS would be your worst case load.
Though now that I look at the numbers, I'm skeptical that this will work as you describe it. I think a bend of that radius will be stretching your 6061-T6 too much. Even if the bar only ends up about half as thick at the middle of the bend, with a radius of about 1.125 on the outside, you'd be stretching the outside by 50%, and the elongation at failure is only 12%. So I think you'd likely crack the outside of your rod before you're done. I suspect you'll need to increase your bend radius, heat the bend area, or both.
EDIT: Quick calc puts the answer around 800 lbs for yielding T6. Probably a bit more than half a ton to actually bend it. O stock, meanwhile, would be around 200-300 lbs and less likely to crack on you. Of course, you'd have to heat treat it after you bent it. On the whole, cutting a 45 bevel and welding the joint and strengthening brace sounds... well... about a half ton easier.