Any locksmith should have them or get them quickly. RV shuuply houses like Tweety's and RV Plus sell them online and they are even offered on ebay. If all else fails, you can order blanks from Trimark.
Most Trimark locks use the same one or two keys anyway and RV dealers often have dozens of them lying around in the sales and service departments. Ask if they have any that match your key number. Some common ones are 743 and 101.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL