NOTE: I DO NOT AGREE OR RECOMMEND the use of Facebook(r) for this as the author has suggested.
Using Facebook(r) will reveal that you are a gardener who has "stuff" AND add you to their database to be sold to someone else... FYI
Other sources are good, although using Amazon will add you to their database of users... FYI
https://apartmentprepper.com/free-or-cheap-ways-to-get-seeds/Find someone who has seeds and either barter for them or pay cash. Don't leave a trail of your transaction which points back at you.