AFAIK, the Volkl pallets will not work. Here are some sources for Head pallets you might want to try. These came from another poster on here.
Ron Bucell,
stringer@thetennisspot.net, has new ones, and can order some in whatever gripsize you'd like, these are PC 600 pallets, with the collars. THese are the hardest to find, he said $15 each plus shipping.
Bob Ray,
tennisray@earthlink.net , has the regular pallets (Prestige classic mid, LM prestiges, radicals, etc...) for $5 including the buttcap.
And Roman Prokes at r p n y t e n n i s has some regular ones and ones with collars in 3L and above.
Hope this helps.