Oh yeah, now this is gonna be good.
Try giving AFA a call, they have Unzan stone, it is just not listed on their website. The prices if I recall correctly were; small $50, Medium $75, large $100 and extra large I think was $150.
Medium is a good price, I think they said those are over 8 inches tall with two pockets for wabi kusa.
Just tell them you would like to order some unzan stone and they will send you a paypal invoice, pretty easy.