I have been making a new garden for the last 4 years & have acquired literally hundreds more plant pots over that time.
I sort mine by size and shape and store them in piles on the bottom shelf of greenhouse staging. That is now well and truly full so I am now completely ruthless about getting rid of the sizes I have too many of or which I will not reuse regularly.
We have a small independent nursery not far away and I asked them about plant pots. She will take any off me that are clean and the sizes & style they use in the nursery. They are so cheap to buy it is not worth their time to clean them up themselves but I don't mind doing it for them because I hate seeing things like that going to landfill.