I've been trying to do this one as well and concur on the pistols.
I don't know how far you want to go, but he has some custom trousers and Jacket too.
I haven't done the vest, but am interested in doing this, when money permits, so will be following with interest!
Being that I'm in the UK, I've been able to see the london propstore's punisher costume and have been trying to track down different parts.
Typically - I've got to ship it over from the states (you guys have all the good stuff!)
Anyway - I've found this to be the closest buckle (looking at the propstores, the exact buckle?)
http://www.strapworks.com/Side_Release_Buckle_p/msrb-n.htm
There seems to be a metal buckle attaching the thigh holster to the belt and two metal ones around the leg straps of the thigh holster, all from the same place.
As for the pistols - are you in to airsoft, as the closest I can find are:
http://www.redwolfairsoft.com/redwolf/airsoft/ProductDetail?prodID=19787
If you look at the propstore's trousers, they have slight pattern to them (sorry I don't know if it has a proper name - ripstop?). Also, both above and below the knee pads is a strip of mesh (from what the extra's in the movie said about his costume, I'm guessing that it was to keep him cool) but it depends on how nerdy you want to get as you could hardly see any detail of the trousers in the film!
I also got a replica of the jacket on ebay - I can't find a list of rules for the board currently, so I won't post links just yet, but here's a couple of 'in progress' photos
(My main issue - need to loose a bit of weight and get into shape! )
(sorry - may need to turn up the brightness to get the detail)
Hope this is of use!
Jon