I can only find one place that sells it, but I'd rather have options. Anyone know of a manufacturer/place to buy?
Get a Lee Classic Loader in .45 Colt and buy or make some black powder... and just roll your own.
A Lee Loader would cost as much as a box of the ammunition you want anyways, because actual black powder ammo is relatively rare compared to smokeless cartridges.
And besides, if you actually do load your own, 45LC is an extremely cheap cartridge to make. Just use either lrn or swc cast bullets (in your choice of weight), your favorite black powder, and some once fired brass. Hell, brass lasts forever on straight-walls anyway, so you might get 10 uses on a single piece depending on your pressures.
Be sure to clean up those cases afterwards, black powder can get really nasty if you let them sit for too long.
you may need an accessory or two for best results.
i.e. primer tool, powder measure/funnel, something to bell the cases, a better crimper if you don't have luck with it's method.