Where can i find stone for a fire pit that I can stack and not have to use mortar?
How large of stones? It all depends what size pit you want, how big of stanes you want, where you want to put it.... etc.
I built a rather simple firepit out of small - medium field stone and cinder blocks. Stacked the cinderblocks, mortared the stone to the outside, poured concrete on the bottom so I can easily shovel out the ashes. It's been there 7 years and people think it looks like a castle. Whole thing cost about $40.
a fairly common very basic version that people use in my area is to buy retaining wall blocks with rough cut edges if you only go two or three rows high in a circle they support very well and were no additional support is needed. My neighbor used blocks 6" thick by 12" wide and about 9" deep ran them two rows high and about a 4-5' diameter and it's been tough enough to withstand scrapes from his riding lawnmower and hits from his boys and there bikes. Looks fairly natural and works great to park lawn chairs around and have small bonfires, if you want smaller and taller you will probably need to mortar