Thanks, u/psilosophist!

I can see how that would work.

This is the closest I could find on Amazon using the search term 'two piece fermentation weights'.

Maybe they're not all that common?

Glass would be better than stone. Although stone would certainly hold my vegetables down!

Your help appreciated :-)

It's 2 halves on top of each other. These: https://www.amazon.com/Gardeners-Supply-Company-COMINHKR057267-1-Gallon/dp/B00ELP36MO/