It would be a lot more practical to spend what funds you have on potted plants at local retail outlets. Or in the case of herbaceous perennial plants or suckering shrubs getting rooted divisions from gardening friends wherever you are located.

look for a plant exchange forum

Can you point me to one?

https://www.houzz.com/discussions/garden-exchange it’s listed in the forums. You need to tell people what you want and where you’re located.

Look at the topics list for anything with the word ‘exchange’. For example, ‘Aquatic plant exchange’. I am sure you will find something suitable.