12v accessory sockets - where to buy.

On a previous fourby, I installed several 12v accessory sockets in the rear for my fluros and the like. They were made of black plastic and had a plastic all-weather cover. They also had a screw on the back, meaning you could simply screw them through the ply. I have spent countless hours online and calling various auto shops, with no luck. Does anybody know where I can get these sockets from. Narva have a similar one, but you can't screw it in, it simply clips in which is not very secure.
Any help is appreciated.