Also a clamp user but there have been times when I buy a shower curtain to use on the picnic table if it has a better pattern than a tablecloth, store bought or home-made.
It isn't that difficult to alter an existing tablecloth to add elastic to the edges like a fitted sheet if that's what you want.
I lust for old fashioned and still useful oilcloth from this company:
https://www.etsy.com/shop/oilclothaddictWouldn't be surprised if the shop's owner would do custom work for you either.