I've bought all my aquarium plants from ebay. You can find either selections or single plants, but I have found one that sells selections (like 50 plants for 20 pounds) and they have been excellent quality both times.
I have used local Facebook groups, local swap events, Reddit on the subreddit “aquaswap,” and finally, I’ve only ordered one plant off eBay and it came in great condition. I know people on here sell, and there’s a specific place dedicated to that as well. Aquaswap is a great place to trade plants and find “plant packages.” I hope this was helpful.
Usually the plants I get from other people seem to do the best, probably because they don’t go through the shipping process.