For the PD31/PD32 24 - mm diameter - there are three diffusers avaialble:
- white cone diffuser: AOD-SO white
- red cone diffuser: AOD-SO red
- new white compact diffuser: AOD-S
The cone diffusers also fit the E25 and E35. The new compact AOD-S diffuser also fits the LD10/20/12/22 and PD30.
As for filters though, Fenix only makes a red filter for the 21.5 size [LD10/20/12/22 and PD30] and red, green, blue filters for the 34 mm size [TK11, KT12, TK15, etc].
Olight make really good filters in several sizes but I've checked and they don't seem to have any close to 24 mm
http://www.candlepowerforums.com/vb/showthread.php?359692-Olight-Filters-Diffusers-for-all-seasons
Nitecore also make filters in several sizes but I'm not sure they'd hold onto the PD32 bezel well as they are 25.4 mm so unless they have some soft rubber like the Olight ones they would fit too large.
The best would be to find all flashlights with 24 mm bezel from other brands and then see if they make a diffuser for that light. I think 24 mm may be fairly common for 2xCR123 / 1x 18650 size but not all manufacturers make filters available for their lights.
Hope it helps.
EDIT: actually the filters for the Olight T25 are 22.9 mm so they
might fit the PD32 24 mm bezel snugly: the Olight filters have a margin of adaptability thanks to the soft rubber used to fit onto the light bezel. You'd have to try one on to be sure though.