Looking to start incorporating band pull-aparts to fix some shoulder issues. Does anyone know a good place to order bands from, or what level(s) of resistance I should use? I know it should be light resistance but that's about it...
Get a miniband from elitefts or jumpstretch.
I've actually been using a 4-foot bungee cord for the occasional pull-apart, but like Pwnisher said a miniband from EliteFts is pretty common and can be more versatile.
What you're looking for is pretty much a big rubber band, you don't need to overthink this. Amazon is fine, as are any of the options above.
If you feel like goin' full eco an old bike inner tube works for me.