This is what I did too. To add to Gordon's notes, if you do go to the insulation contractor's supply, please don't try and ask to buy half a roll !!!!! Anything that is too much work for them will likely result in you being denied.
I went to Behler Young here in Michigan. Called one of their branches and the lady said no way, then I called another branch, got in touch with a cool guy, and he okay'd me to buy two rolls on Linacoustic. I told him that it was for a home theater. They did say that it technically was for wholesale only, but since I was buying a whole roll (actually two), they didn't seem to mind.
Also, I paid in cash too. It was a quick and easy sale and that's what I believe they'd prefer!
Good luck!