I have filter wheels here for the Aminco Bowman Series II. I am not going to lie, they have not sold well at all. The can be used used for basic polarization measurements and special filters can be installed but people don't seem to really want to do this. I have to charge for them as I need to cover my time with billing and shipping but if you are interested in obtaining a pair of them(or one) you should not fear a high price.