Frankly, I am unsure that there is a knife maker of any note in Chiang Mai. Refer to this Knife Depot blog post from a couple of months ago titled Buying Knives at the Chiang Mai Night Bazaar. Daniel Lawton — the author of that post — evidently lives in Chiang Mai, so he should be well-placed to know.
However, a poster on BladeForums.com stated in August, 2010, that Chiang Mai does have knife makers — but perhaps they are mere hobbyists? Nonetheless, not this brief blog post from March, 2010, titled Picture: Knife-making. It is a shame that the shop was not at least named.
I know Bangkok has noteworthy knife-makers, one of whom opened up a shop in Udon Thani a few years ago — note this UdonMap reference for Yuna Custom Knives. A forum thread developed in November, 2007, because a forum member mistakenly thought the shop had closed: Yuna Custom Knives.
If anyone has concrete information about a knife-maker in Chiang Mai, let me know, and I will happily update this post!