Danny,
I have read about making stein bier, which is similar to what you described. The homebrew club who did it (and were featured on BasicBrewing), said they got their granite from off cuttings from a tombstone maker. You could check around town and see if there are any businesses that do that sort of thing.
Here is a link to the BasicBrewing archive that has the stein bier show (Nov 10, 2010):
http://www.basicbrewing.com/index.php?page=videoTom