The easiest way to get a hold of one of these spectacular stones, is online.
Here are the online retailers we can vouch for:
Buying in Store
Depending where you live, this can be trickier. The best bet to find a local store would be to look for a shop that stocks 'Crystals' in your local are on Google.
Contact them, see if they either stock it in store or can get it in for you.