Hmmm, I could have sworn I bought a three way swivel from Dive Rite. Well, no worries, Oxy Cheq has them:
Fittings-Swivels
I have seen them other places. I just gave my spare to a buddy or I would have given it to you, sorry.
The screw "thingies" that Luis has there are probably from McMaster Carr, google them and you will find zillions of screws and springs and nuts and fittings and all sorts of strange hardware useful for everything from lawnmower to your scuba gear.
I am happy to hear that I am costing you money. A few weeks ago I sneeked off for a quick dive adventure, a mini trip, I like watching people when I rig up, they often don't say anything, but they do LOOK. It is no big deal but it is funny to observe them during surface interval, they are afraid to ask because as you know guys don't like to ask questions because it is an admission of weakness (a a guy thing ya know) so they cannot satisfy their curiosity and it frustrates them. Then when they finally work up to it I have to disappoint them with, "no, you cannot buy one like it, no, that is custom made by XXXXXX, no, I made that and I only made one, no, they don't make those anymore but you can get parts from vdh.com, no, I got that from a friend and there are no more, no, they quit making these 30 years ago" etc. They almost cry. AND, as you are finding out, it costs a lot of money and time and effort to duplicate some of the rigs you see vintage divers or "eclectic" divers using because they are a mixture of items you cannot simply call up scubatoys.com or leisurepro.com and be satisfied.
There is a thread up in the BC section about plastic plates, he wants one. I have given all of mine away except for the ones I use and want to keep or I would send the poor fellow one or two but at least in this case those are plentiful but a few of the most gooder ones are hard to fine--lol.
N