You could probably go with something like this:
B86-02-2 (405E) | Euro-Locks a Lowe & Fletcher group Company, L-Handle Locking Handle | RS Components
TBH, though, I'd recommend going with the Lintran OEM option.
Not only are they a great company to deal with, and who deserve support as a strong partner to shooting, but if you ever look to sell the dog box it will likely be much easier if you have the Lintran handle/lock fitted. Otherwise people will just expect a discount.
You are likely to be saving pennies by using a generic version, so why risk your dog for that?