Looks like there may be a name on yours? I can barely make out a letter ... it seems like a 'D' for Attwood.
But MANY make these and they are not entirely interchangeable amongst brands.
Attwood, Cabelas, Cannon, Roberts, Scotty, etc., where I believe Attwood bought out Roberts and Cabelas are made by Scotty - where those pairs usually interchange.
If it is indeed an Attwood ... I may have a bunch of spare mounts and holders I could sell you.