The boots are Canadian Military Muckluks. I lucked out and got mine from a guy on the old Blizzard Force boards before they shutdown. If you need boots I'd suggest either Ebay or go digging through military surplus websites. For sizing get about 2 sizes smaller than you normally would as these boots are huge. I'm about a US size 10 and got size 9 boots. I can actually put them on over my shoes they're so big. This is actually a fairly standard practice with snowtroopers and is kind of nice in the comfort sense. I took out the wool liners since I don't need the boots to actually insulate my feet.
The boots are fairly simple to convert. Remove the laces and the lace rings, you can leave the lace around the top in or remove it, both are accurate to the movie but most troopers leave them in.
For the bindings I got some off-white cotton webbing at Jo-Ann's. After sizing the strips around my legs I sewed 3/4 inch velcro on the webbing and then riveted the webbing on to the back of the boot. I'm not sure if the direction of the straps matters as most reference material I've found doesn't seem to show any pattern. I made my straps close inward so that the boots were mirror opposites of each other.
The straps I used aren't movie accurate as far as the texture of the strap goes but I thought it'd look better if the straps weren't bright clean white while the boots were dirty tan.