My new enlarger necessitates 6" VC filters to fit between the condenser glasses. I've currently got a set of Ilford 3.5" filters and I'd love to find someone who happens to have 6" but needs 3.5".
I know, I know, that's like meeting your future wife in a bar... but hey!... it could happen.
I also have a Kodak Polycontrast set, same size, that I'd throw in, incase you needed to cut up a set for another use, or something. I have lots of random stuff that I'd be glad to trade for, just let me know what you're looking for.
Alternatively, I'd buy a set for less than $25 (cheapest set on eBay).