I was think of getting a filter for infrared photography, the B+W 092 MRC (Multiple Resistant Coated)
http://www.bhphotovideo.com/c/product/591341-REG/B_W_1057385_40_5mm_092_Infrared_IR.html
BH Photo and Video seems to be the only retailer In North America that carries this filter. That is Problem #1 (it is a US retailer and I live in Canada).
Problem #2 is the filter for that thread size, 40.5mm, is special order only and could take a long time and there are no refunds. They do have the 52mm version in-stock, but it is more expensive ($15 more) and I would need to use an adapter to put it on my camera as the lens has a 40.5mm thread.
Problem #3 is that if I ever get a Micro Four Thirds camera, the 40.5mm version could become obsolete as there is only one m4/3 lens so far has a 40.5mm thread. In contrast, there are four m4/3 lenses available that use the 52mm thread (the rest range from 37mm to 58mm). There is no guarantee I will buy a new camera anytime soon though.
I have little experience buying filters, so I ask: should I just special order the cheaper 40.5mm version that fits my current camera perfectly, or pay extra for the in-stock 52mm version that might be more usable in the future?