They are Catappa tree leaves, native to southeast Asia. I doubt they grow in the US, unless maybe in the far south. So no, you probably can't grow them yourself.
If you use them solely for the tannins, you can use oak or maple leaves, almost any hardwood leaf, that's turned brown. Oak is nice, they last and since the trees tend to hold the leaves long after they go brown, they are usually relatively clean.
If you use them for their antibiotic properties, I don't think there is a substitute.
I should have said, been using them for a couple of years and I like them. I use them for sick fish, fin rot and my Bettas, and currently have a few in a tank where I am hoping my Daisy Rice fish will produce some fry, in hopes the rotting leaves will be a source of infusorial first food if any fry hatch. The darn fish spawn daily but the eggs take 3 weeks to hatch and are crystal clear, thus I can't ever find them to check on.
They leach a LOT of tannins at first, but they don't last a really long time. They rot quite quickly. Oak leaves, OTOH, seem to last a lot longer, but with a lot less tannins.