I can't find the reference in a search, and as I think about it, this might be lost to the Blue Void. I recall reading that he had these made after winning the Main. Maybe for his home game, maybe for a souvenir of the event??
I have a set like the one you have. Started that over 10 years ago and had to get them one at a time, with the $1000 was the hardest to get. I've seen the group of four on
eBay a couple times in the last year. I presume yours was from the one that ended not too long ago.
Available in quantity? Almost certainly not unless someone has been hanging onto the set Fowler had made and only recently started piecing them out.