I find it slightly ironic that you live in a town that has:
two outlets for each of two chains (JoAnn's, Hancock), one alterations shop that has about ten bolts of fabric from 1960, and a host of upholstery fabric stores
...yet you cannot find hair canvas.

I live in a town where there is exactly one (1) small, locally owned fabric store (besides the meagre selection at Wal*Mart, whic I don't count). And they have hair canvas. Several kinds, as a matter of fact.

On the other hand, my wife was visiting relatives, and there was a large chain fabric store having a major sale, so she was stocking up on supplies she knew I used. She couldn't find any hair canvas, so she asked a sales clerk, who never even heard of it. Go figure.

Now, finding ulholstery thread locally in a selection of more than three colors is what I have trouble with.