Stone blocks are all over the place in Krokotopia (especially the Ice and Storm pyramids). You can also find them in Marleybone (I like Knight's Court) and in Grizzleheim. You can also get it by gardening Dandelions and Fickle Pickles.
Here's a link that shows you all the places to get stone blocks.
My favorite place to get stone blocks is Crab Alley. All I do is loop around, beginning at the entrance, and switch servers until I have the amount I need. You can also find other ingredients for crafting recipes down there - the kelp and shells are good to pick up there, and that's a pretty good spot to get both at an early level (before having access to Celestia) - which helps with later crafting recipes.
My personal favorite farm spot for Stone Blocks is Caliburn in Avalon. It's a nice open area with three spawns (and a Cat Tail if you want that), then you can switch realms and get them again and again until you've gotten enough.
Depends on what else you need, honestly. The Necropolis in Dragonspyre usually has 2 per realm, but it also has lava lilies and deep mushroom, and it can take about a minute to run across the screen to collect everything so you don't have to watch the timer count down. I've been running around Stone Town in Zafaria recently - it's got some black lotus and some sandstone, which is nice.