As a Proxy for the Summoned Stone s I ordered these Shifting Stones published by Privateer Press:
They are readily available in at least UK (online) shops, and I ordered mine from Wayland Games.
I like this style a lot, really fits Descent as it sits in front of my mind's eye, even though they differ completely from the artwork (and corresponding Shapeways offering, which is beautiful too).
Only caveat is that some may find them too large, the base is 30mm and I suspect the height (without base) is around 30mm too.
So I may rebase, unbase, or try something else. Other than that, I think their height will add real presence to the game board.