If they look like this and have two little contacts on the base and the pins on the sides of the barrel are not at the same level, they're standard 1157's. Available at any auto parts counter, WalMart, etc. If you go to the RV store, they'll be a lot more expensive for the exact same part.
It's recommended that you give the base and contacts a light coating of di-electric grease to prevent corrosion. Clean the socket well, too.