i would jsut replace the whole axle.... some people have good luck with replacing the boot, and some dont... the only way to be sure that joint has proper grease and isnt contaminated is to replace the whole unit... once the boot tears, there is no way to tell if any damage was done being run low on grease, or contaminants entering it.
if you still wnat to replace it, they are fairly cheap.. they come with a clamp similar to a hose clamp, but it is a 1 time use clamp, like a band clamp, and a pouch of grease -- are availalbe at any local parts store
