I'm going to say that it is very doubtful that you can acquire rabies vaccine. I'll explain why.
Last year my son, who was 4 years old at the time, managed to pick up a chipmunk by the tail. In the process, the chipmunk managed to give him a nasty little bite. I arrived home about 15 minutes after it happened, I couldn't track the chipmunk down so we were left wondering how the boy managed to catch the chipmunk if it wasn't sick. He was playing very loud in the yard, yelling and screaming and just making a lot of noise (which also made me wonder how he caught the chipmunk with all the nosie).
So I started doing some research, small animals die very quickly they contract rabies (this includes squirrels, chipmunks, rabbits, et cetera). Connecticut (and other states as well) and the CDC have infection datasets available for download. These datasets are have several interesting datapoints including county (some have greater geo data as well), animal type, reported infections, and some dates are available as well. I found a few cases where rabies was transmitted from a chipmunk to a human (none in CT). This was enough for me (my threshold was one).
In the morning I called down to our doctor, and was immediately dismissed "Rabies doesn't transmit from small animals to humans, the statistic is within an acceptable measure."
So I called the State of Connecticut epidemiologist. I explained the incident with my son and where we lived (our house borders a local forest/tree reserve). She was very nice, and spent about 20 minutes talking with me about rabies and cases in the state. She explained the cases in our area (including several within the last few weeks). She mentioned that statistically, it's very unlikely that my son was infected by rabies, however, she said "I just can't see a four year old being able to catch a chipmunk."
She explained that all of the rabies vaccines in the state are controlled by the department of epidemiology and are correlated with the infection data both locally and nationally (CDC). The vaccines are very expensive, very limited and sensitive to expiration (apparently they don't last for years). She told me the process for obtaining the vaccine was a formal request from our healthcare provider (i.e. I couldn't just buy one).
So I asked her what she would do, her reply "Get the vaccine, the circumstances are just too strange and we have no way of verifying without the chipmunk.", and because the administration of the vaccine is very time dependent (I believe it's 72 hours). She told me to call the doctor and have their office call the department of health (epidemiology) and speak to her if they had questions about the specific data.
I spent the next several hours debating with the pediatrics department. They kept insisting that since the statistics didn't support it (no confirmed cases in CT), that it wasn't relevant. They did acknowledge that a few cases have occurred with squirrels and rabbits, but none with chipmunks, so it didn't matter. Eventually, after working my up the chain (keep in mind this is at an HMO), they head of the pediatrics department let it slip that the vaccine ran about $7500+ (presumably because it needs to be administered over the course of a month).
Now I imagine that you can probably obtain the vaccine from a number of places, but in an official, legal capacity it appears that the vaccine is extremely expensive and not likely to be available in any SHTF case.
I'm not saying this is the case everywhere, but is absolutely the case in Connecticut and it wouldn't surprise me (since the CDC is involved with ALL rabies cases and vaccines) if other states were equally stupid in this regard.