Both the Caliburn in Avalon and Twin Giants in Azteca are great scources for stone blocks. However, if you're not able to go there yet, I suggest looking in certain places in Krok, mostly in the Pyramid, the Krokosphinx, and the Tomb. The quantities there might be better or worse, but its a much longer route. But now thinking about it, if you're impatient, lazy, or have plenty of gold, you could always camp out in the bazaar.
Krokotopia, usually along the walls. Best places are the Sphinx and the Tomb of Storms.
Marleybone, usually on the rooftops. If I recall correctly, Knight's Court and Chelsea Court had spawning points around the teleporter hubs.
Mooshu, usually along the roads. The Cave of Solitude had the most stone blocks.
Dragonspyre, usually along sidewalks and in back corners. The best two spawning locations are the Athenium, and the Necropolis just behind the Crystal Guide.
If you're doing the Marleybone crafting quest, I'd advise you to go back to Krokotopia and sweep through the Tomb of Storms, especially the Ahnic and Djeseret tombs - stone blocks spawn along the walls and in most end areas. Once you've cleared an area, change realms and do it again. It won't be long before you've gathered as many stone blocks as you need.
Stone blocks can be found in all areas of Dragonspyre. There are a couple of spawning points in the Atheneum, The Academy, as well as the other streets. Those in the Atheneum will always be behind the library and Ore can be found there as well.
The ones in the Academy will move around to other spots but once you find them, which will be 5 spots total, you can always find 2 in every run by changing realms after each run. Ore for trying to get diamonds has 6 spawning points but will only spawn in 2 in any realm. The only time you won't find them is if someone else is also running those same areas.
Marleybone has a few but they are on the roof tops. The main reagent in that world is Scrap Iron and Mistwood.
If you're talking about the reagent, then it's in pretty much every world, scattered across various streets. I believe they most commonly spawn in Krokotopia. You can buy them from a reagent vendor or bazaar as well.
Stone Blocks can be found everywhere in the Spiral. Some places do not have it, either a player already collected it, or it just needs to regenerate naturally. If you need exact locations, I suggest checking out the Wizard101 Central Wiki for a full list of locations where Stone Blocks spawn.
If you're a lower level or any level a great place is Crab alley. I did a lap around the place switched realms, rinse and repeat and by the 6-8 time you should have 20+ Stone block. But its all random that's just from experience. Hope this helps :)