Why didn't I think of that, lol! Thanks Charlie_R!

bellini - I checked on Amazon, and all 3 of the products listed as the Unicel c-4313 are pleatco's or another substitution. It does look as though Amazon sells the Filbur FC-3753 (2pk for $15.35 - although the picture doesn't look like a Filbur, the description says it is a genuine Filbur). The other one for Filbur says it is sold externally through Filters Fast (2pk for $9.97 + $5.97 shipping) and on their website they say they are genuine Filburs as well.

I'll pass the info on to my SIL so she can order some for her pool, best of luck to you on your pool as well!