I think they are out of production.  If you look around you can find the filter parts, but the rubber part seems to be almost impossible to find.  Too bad, that was a great product that fitted my needs exactly.   The blue line filters worked well, I would ca them together and then put some heat shrink tubing on the outside, after that they never would come apart.

In the r/c car section at your hobby shop you will find air filters for the fuel engines that are useable though larger than the Bru-Line type.