There are quite a few internet sources for both the blanks and the keys themselves. If you know your key number, you can just order them.
If you don't know your key number, you can order blanks, too.
Here's one source that my Sunline friends have used with good results:
http://mysecuritypro.com/rvandcamper.aspx
There are many others. Search on:
rv key blank or try searching on the lock manufacturer's name.
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'11 Cougar 326MKS loaded with mods
'12 Ford F250 SuperCab 6.7 PowerStroke Diesel
Amateur Radio: KD2IAT (146.520)
GMRS: WQPG808 (462.675 TPL 141.3)