B&H, Adorama, Freestyle. This is something you want to buy new, they do fade over time and you want the best you can get. They aren't that cheap, but worth the price.
I have a set that you can have for the cost of shipping. The only caveat is that several of them (1.5, 2, 2.5, 3, 3.5 and 5) have been trimmed about 3/4 of an inch on one edge. I don't know why, I got them this way. I'm never going to use them; I use an under-the-lens set.