These are just normal camlocks available from any rv store. Come in 2 different lengths I think 7/8 inch is the right one. Try to get them all keyed the same for convenience. They are very inexpensive. probably under $5.00.
The spares I have in stock came from vintage trailer supply and are called baggage door locks. Prime products # 18-3045
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The lock smith just doesn't want to be bothered as these locks are very easy to pick. They are also so cheap to replace it doesn't make sense to use a locksmith anyway.
If you are able to reach the backside of the lock in the compartment from inside the trailer just remove the screw (Phillips?) that holds the cam and you will be able to open the compartment and remove the lock assembly to replace it.
Been there , done that