I see them on ebay fairly often and I think
http://www.rockauto.com has them. Most local parts stores either carry or could order a kit up for you as well. These carbs are not *really* complex, but you can make a fair mess of it if you are not prepared very well. I've never had to tear any of mine down completely, but I've opened one or two up and got them back together working as well as they did before I started. My trick was just to take it apart and have it back together before I forgot what I was doing. Its when I have to set a project down for a few days and come back that usually gets me.
Digital cam pics are a huge help, take plenty if you have one. Its worth paying for prints probably if you don't have one. Buy cheap film and develop it only if you have troubles if you really want to pinch pennies.

I seem to have better luck with a good hosing down with Seafoam DeepCreep cleaner than I do with opening things up though. Solved more problems with that stuff than most of my tools. Hose the carb throat, spray a fair bit down into the bowl overflow tubes, blip the starter to suck a little down in the motor, hose the carb a bit more, let it sit for a half hour, and then go for a 5-10 mile highway drive. Works just about every time for me.