We sell two sizes of Polarizing filters for visual use with the Herschel (both are produced in Japan for Baader Planetarium). The 1¼" version can be threaded onto an eyepiece directly. The 2" can, of course, be attached to a 2" eyepiece.
Please note when used with a Herschel Wedge Solar Prism: Polarizing filters are intended for visual use and must only be used in conjunction with the existing internal ND=3.0 filter. A polarizing filter does not provide sufficient blocking by itself, nor is it able to block IR wavelengths as completely as an ND filter. Also, the polarizing filter must be used on the eyepiece or eyepiece reducer, never ahead of the ND3.0 filter (the polarizing filter must be located after the ND3.0 filter to prevent damage to the delicate internal layers of the polarizing filter).