Unfortunatelly, Pollenex no longer makes filters and parts for their systems.
All of our o-rings are located here:
http://www.waterfilters.net/Parts-Accessories/O-Rings/O-Rings.htm
These are pretty standard sizes so it's possible that one of these would work for this system. You can measure your current o-ring and compare it with the measurements of these o-rings.
What size filters does your unit use? We have a cross-reference for the WP52 model but I'm not sure if it is the same as the WP52B model that you have. The cross-reference for the WP52 model says to use the C-1 filter cartridge:
http://www.waterfilters.net/culligan/wholehouse/replacement_filters/C-1.htm
A lot of housings that use the C-1 filter use one of these 2 o-rings. One of these might work for your system.
http://www.waterfilters.net/Culligan-Pentek-OR-34-O-Ring_p_0-191.html - standard housings
http://www.waterfilters.net/Pentek-Culligan-OR-38-O-Ring_p_0-192.html - slimmer housings
If you can't find an o-ring dimension that matches, your best bet would be to buy a new system such as the Culligan HF-360:
http://www.waterfilters.net/culligan/wholehouse/housings/HF360.htm
Thank you,
WaterFilters.NET