As said in the title!

where to do a volume purchase of go stones? the cheap the better... as long as they don't brake by looking on it

Try 6Brothers in South Korea. They were recommended in another post here and they sell all sorts of equipment, not just high level. I think plastic stones would be cheap and possibly more durable than glass.

You didn't say in what country so shipping could be more than the stones are worth. If this is for a go school session, use anything that is practical and cheap like simple hardware washers and just spray paint them white and black. If you are in the States, try baduk.club who also supply inexpensive folding boards.

If you are talking about getting many sets of stones (such as for a club), 6 Brothers in Korea is the way to do it. It helps if you have somebody who can write them in Hangul (Korean). They can do surface shipping, which takes a while, but keeps the cost down. In the past they wanted payment by international bank wire, which was $45 in 2018. The shipping limit is 20 kg per box, so the most efficient way to ship is to come in just under that limit.