Gandasaputra, try contacting Phonak (http://www.audeoworld.com/) and see if they're still selling those filters.
had contacted the person and sadly the representative replied:
Sorry if you are unable to find them on:
then we are out of them indefinitely.
Apparently since the phonaks are discontinued, so are the filters. Oh well, I'll stick with the green ones but it'd be great if I could trade some of my greens with the grey ones.
I'm in the u.s. and have been looking for some spare grey filters. I haven't found any. earphonesolutions and audeoworld have been out for a long time. Your best bet would honestly probably be to sell your pfe and buy a set with grey filters. :-P Or hope they show up on ebay or something...