I've not had the fortune of meeting Pak Mat of Kg Baru. I'll be up in KL next week and would try to find the time to do that.
The Central Market is another story. I think the prices are overblown, even by Singapore standards. I would suggest you drive a hard bargain. Put up a thick skin and ask for one third what the shop is offering!!
If you're in KL on Sunday, check out the flea market at Ampcorp Mall in Petaling Jaya. Great cultural stuff at bargain basement prices (the flea market IS in the basement
). Many keris collectors and dealers congregate there in the afternoon, including some of our esteemed members in this forum.