looking for a local bar

Where should I go shopping for a chin-up bar that fits in a doorframe by compression? I expect there's some kind of spring involved, and maybe a way to adjust the thing in the middle as well. I want one that will fit a doorway about 33" wide, without damaging the doorway enough for my landlord to notice. I say "about 33" wide" because I intend to put a thin block of plywood between the end of the rod and the doorframe, so the end of the rod won't dent into the plasterboard...and I don't know how thick the plywood will be, because I haven't bought it yet. I'm not talking about a wooden "doorframe," here, I'm talking about the gap in the wall outlining where one might put a doorframe and a door.

Don't worry, I'm not planning to actually do any chin-ups. I want the bar to support heavy insulating curtains. The objective is to keep air in my living room so the little air conditioner has a fighting chance. (Presuming, of course, summer ever comes.) And, if possible, to put a bit of sound insulation between me and the neighbors on the other side of my thin bedroom wall.

Any suggestions for the bar? (Or should I call it a rod? The names are "chin-up bar" and "curtain rod," even though I'd have thought the cylindrical shape more critical for chinning.) Or suggestions for finding heavy insulating curtains in May without needing to ship them from New Zealand or something? Someplace on the Red Line, or near Arlington/Somerville/Watertown/Cambridge. I can drive if I have to, but would prefer not to drive all over creation.