If you have the original rear, it shoud be an 8.2" not a 7.5". If you don't have the original rear than I guess it could be 7.5".
The aftermarket sells 12 bolts, 9", and Dana 60s and maybe even 8.5" that are either cut down or freshly made to fit. Think Moser, Strange, Currie, as well as others.
To get a complete aftermarket, ready to bolt in, expect to spec $1,700-$3,000 depending on which you choose and how you have it configured.
Early full-size Ford rearends from the wagons or full size sedans are supposed to fit (1958-1960), but will need a re-fresh, gear change, brake change, new spring pads, etc, in order to install. If you are clever and do some of your own work figure this would cost $500-$1,200 without having to cut down the axle., but try to find one.
Likewise above for early Ford Bronco's, some of these are supposedly bolt in swaps, but you would likely still need a posi and gears as well as brakes.
One other option is a later model Lincoln with a 9" - some of these even came with disc brakes. Factory posi units and gear selection considered not too good for high performance. there is a guy out of Columbus who has listed these on E-Bay for $1,200-$1,500.
A couple have successfully installed 8.5" rears from Chevy S10s or Sonomas. 2 wheel drive models with the 4.3 V6 apparently had the GM 8.5" rear, some may have even had disc brakes. There is a seller on E-Bay out of Florida who has listed these for $800-$1,200 but as i understand it they are a little wider than the stock axle, which is already about .5 - 1.0" too wide.
Which brings you back to considering how much power you will be making and maybe considering upgrading your exsisting 8.2" with a new posi, gears, and Axles. This will cost roughly $900-$1,200. Check some other listings on this site as one of them has a link to a Chevy high Performance article on this very upgrade for a mid-eleven second nova.
By the way I am still running an 8.2" rear.
dan