The rocks used are actually barnstone which can be found at most stone yards. Most commonly they are reclaimed from old barns being taken down and were typically used as the foundation blocks. I uploaded a couple pictures where you can see them being used as fountains and the wall in the background is the same barnstone material. The stone is then core drilled and plumbed in a series configuration. Any stone can work in this application if you have a stone core drill bit and an impact driver. Basalt would also be a great alternative which is readily available online (Pre-Core Drilled) and is exported out of Canada. Do a search for basalt fountains and I am sure you will find what you are looking for.