They finally patched it... you could clear your 360 cache. Don't ask me how to do that one. once you do clear it disconnect yourself from live, so you don't re-download the patch. and try the glitch

The staff store is in the market district and its on the outer buildings unless its the staff place thats across from the magic emporium. Is it for a quest? Download the FrostCragSpire, it has several Grand soul gems. It should be free by now. If you give me some time I could think of some more place to find gems.