I destroy big rocks to get 1 stone

[Kiz]

How do you get so many stones?

[Ardele]

Level up your harvesting skill but followers that specialize in harvesting with bonuses will do a better job.

[Kedryn]

There's a patch on the preview branch that lists this as one of the fixes:

◍ Fixed not receiving any stone when mining from rocks.

[Tanyon]

I would recommend bringing 2 followers with you and have them do it.. they do most harvesting jobs way better than you do.

[BenchWarmer]

Stones are usually all over the ground, wherever Rock is. To get more than you'll ever need, setup a Mining Camp and let one of your villagers mine Tin, Copper, etc. They'll get lots of Crude Stone too.