Hello,
I can make you a bot to automatically post any number of products directly from your database, to FB Marketplace. I have done similar bots, and I already know how to work with FB (public and private apis).
Then you can run the bot by your self or contract some one to handle it.
As FB Marketplace is intended for human usage, and also only for USA, you will need several accounts if you plan to post a big number of products, also several IPs. I can also sort all of that for you.
If you are interested let me know and we can discuss it.
Regards,
Octavio.