Hi Kevin,
This topic came up a couple of years ago, so I started looking at ways to buy plain old talc. It is available in bulk through chemical companies, *Bay, and other sources. It does take a bit of looking, and you have to be willing to buy more than you need "right now." I'd split the package with a peer...if I had one nearby.
J&J stopped using talc a couple of years ago in the US market (those "ads" you see on TV for "do you or a loved one have, or ever had uterine cancer? Call us now for class-action law suit..."). Their latest news was to drop it world-wide this year.
I'm not sure of the differences, but older threads here indicate zinc stearate (ZS) is a usable substitute. Randy Smith jumped in one of those to mention he sells (sold?) ZS . I don't know how talc and ZS behave differently with respect to our intended uses. My really old Equate-brand Baby Powder (23 years old) did the job as expected the few times I used it. I still have quite a bit left in that old bottle, and may be able to discern what the components are. I do know I can't find the exact same packaged stuff. Same brand, different markings...so I wasn't going to buy a bottle to test since my kids manage their own backsides now.