The keys are almost universal - there are only a few different key codes for most RVs of that era. Look for a number on the lock. CH751 is one common key; 9901/MMK is another. You can order them online or buy on Ebay, but most likely an RV shop will just hand you one of a dozen they have lying around.
Most RV dealers, RV techs, and even campground offices have a set of the most common keys. Most any of them could help you out, but it's easiest if you know the key numbers.
More unique locks are available now if you are worried about this, but most people don't really have valuables in their RV anyway.