I’ve never seen the hardware for the rail available as spare parts but others may know differently? I used to make the bits on a milling machine to fit the rail I was using. I used to use Anschütz rails as these were commonly available as a spare part. I generally used M5 cap head socket screws (black or stainless) for clamping everything together. Making the wooden part is easy but can be a bit tedious if you go for a stippled finish like I did. Good luck with the project.

No idea on the current ISSF rules but you should be able to download a copy.