As it's over a week since you posted, I wanted to say something!
Due to the way the wallet is constructed, I think a replacement is almost inevitably going to be required if you use it much. My own started wearing out quickly, but I realised that I never performed the trick (I carried it with me for ages, but never felt the time or audience was right for it). As such, I never tried to replace the wallet.
I doubt you can buy replacement wallets on their own (but ask at Alakazam, they are very helpful).
As there are two elements to the wallet, a direct ready-made replacement is probably asking too much. You could, with some thought, adapt the method a bit and/or use an existing magic wallet, perhaps one that you've done some work on.
This might give you one way of proceeding:
http://www.letteringonthecheap.co.uk/sp ... ering.htmlThe trouble is, for the trouble and expense you'd go to to make your own version, I think you could be better off buying the whole trick again. It's currently on sale at Alakazam. Maybe you could suggest they offer spare wallets when you order.