I bought a Crimson Trace Lasergrip for my Kahr MK9 from an eBay seller. Unfortunately, they didn't fit since I have an older version of the MK9. The seller allowed me to exchange them for another model with no issues.
They are one of the cheapest retailers that I've found. Customer service was excellent and they were very responsive to email. They also have a website. They went on vacation for two weeks, so I thought I would have until they received my exchange before sending out the new one. Nope, as soon as I sent them the delivery confirmation number, they sent it out that day. One of the best eBay sellers I've had the pleasure of dealing with.
AgriSports Inc
Even their eBay feedback is impeccable.
eBayID:
eBay My World - pistol-lasergrips