I think autozone sells new boots in a "caliper hardware kit". Unsure if they have them though as i haven't checked.

Usually, for maintainence, what i'll do is remove the pin and boots, clean out all the grease, and then reapply high temp grease to the slide pins and work them in the sockets a few times. Then, i'll spread some inside the boots to try and seal out water and then reinstall everything.

The front setup is the same, but the caliper is clocked up higher out of the way of most water, plus th front brakes get hotter as they do the most work, so water tends to evaporate very quickly. The rear brakes sit lower, and tend to not get as hot, so they can have water sit on them for a while, and that will start to corrode them out, as i've noticed mine starting to