I got mine from Amazon. They usually have a wide selection, and you can read reviews from other RV owners to make sure you're getting a good product. Just search for
filluck rv door lock set and you should find several options. Amazon is not the only option here, this i can guarantee, you can also check official website and i think that you could find some more stuff. I must add that installation was pretty straightforward for me, but it's always a good idea to read the product description and any customer reviews to see if others have encountered any issues with installation or compatibility.