Stone is probably the easiest resource to gather in Valheim. Within only a few hundred meters of my Meadows landing zone on a new continent, I found somewhere on the order of 2500 stone. Like others have mentioned, the Black Forest, the Plains, and the Mountains have more stone. But the Meadows still has a lot of stone per hectare. Probably the only place that you'll have to import stone would be the Swamp.

Rocks are nearly everywhere underfoot, and even the small ones yield five stone. That doesn't sound like much, but considering that it'll take, at most, two hits from a good iron pickaxe (you do have an iron pickaxe, don't you?), that small change will yield big dividends if you seek them out. Ten of those small rocks, that are literally everywhere, you now have a full stack. Big rocks are going to yield 25. The big plates, like what you'll find in the Black Forest, yield hundreds of stone.

I cannot stress enough how helpful the Megingjörð belt is when gathering stone. I can carry about three and a half stacks of stone, probably more if I de-gear with the belt on. But if you don't have the belt, it's easy enough to just create a stone pile with the hammer, and then run and grab it when you run out. Alternatively, the cart can be a big help in gathering stone, if not to bring it to your work area, to at least keep it all together and safe so you can run back to it frequently.

It takes me no more than five minutes in a new area to get three stacks of stone. But you have to care enough about gathering everything underfoot to make this happen.