I did a little search and there aren't any used Future Spa glasses popping up at the moment. There was that one on e-bay a few months back. And one in England that the auction was ended two months ago. So your best bet is to contact Mayfair as was mentioned earlier, or be real patient.
I myself haven't broke any pinball glass yet after having handled probably hundreds of them.
Sucks that you did.
But as I always like to say "better you than I"