M/39s are usually known by the factories that produced them. Those are long Finnish names, but are abbreviated to "VTK","Sako", and "Tikka"(which are very rare). There are also some special varients: "Sk.Y." is an abbreviation for Civil Guard, "B-Barrel" indicates those M/39s that were built with Belgian made 91/30 barrels that were cut down. All of those were made during WWII except the so called "Sneak" rifles. These were make in the late 60's and early 70's basically out of spare parts.
You can learn about these interesting rifles here:
http://www.mosin-nagant.net/finnish_mosin_nagantm39-Part1.htm
The rifles will usually be listed using those names by most vendors. WG&A sometimes does not list all the variations they have in stock. I'd call them and ask if they have what you want. I got a beautiful unissued condition Sk.Y from them by calling and asking. It wasn't listed in any of their ads at the time.
If WG&A doesn't have one, you could also try the gun auction sites. I've seen them now and then on
www.gunbroker.com and
www.gunsamerica.com.
Edit: WG&A does currently list Sneaks on their site, they just don't call them that:
1967 UNISSUED.........................$249.99
1969 UNISSUED.........................$399.99
Yea, pretty pricy, but these should be in brand new condition. If that's too rich for you, I'm sure one of the $150 "excellent condition " VTK or "B Barrel" rifles would shoot very well also. My B barrel is the second most accurate centerfire rifle I have, only beat by the Sneak.
BTW: You guys without C&R licences need not be left out. On the bottom of their M/39 page, they list a few of these rifles that are considered "ANTIQUES BY THE GUN CONTROL ACT OF 1968". These are made on late 1800's recievers so you may purchase these without a licence and have them delivered to your home, assuming that is OK with your local law. Pretty cool huh? Just do me a favor and don't sporterize them! These rifles deserve much better than that.
Here's the link again. Keep an eye on this page, the inventory changes often:
http://www.gunsnammo.com/index_files/m39.htm