[disconnekt]

You can always try seeing if your local community college has a photography department (especially film classes), and see if you can put up a list of the filters that are geared toward B&W film & sell them to the students there.

[BrianR]

Pop the glass/plastic and epoxy them front to front to make reversing rings for macro.

If they are different sized filter threads, you can epoxy them together to make step-up or step-down rings.

Or keep the glass/plastic in and draw on them with black markers for special effects - you can make weird shaped apertures this way (stars, hearts, clovers, ice cream cones, etc) for the out of focus highlights, or you can make your own split filter where half the filter is black for non-overlapping multi-exposures (rotate it 180 degrees between shots). You can also smear Vaseline on them for the soft focus glamour effect.