Does anyone know where I can get another linkage coupler like the one that is hooked to my throttle in the pic below so I can get my choke working?
Been there, done that. The proper term for what you seek is: "throttle ball joint". http://www.dormanproducts.com/c-213-carburetor-throttle-ball-joints-linkages.aspx
Just pin or wire the front choke and use your existing rod on the rear choke. You only need one functioning choke, even in the coldest climate.
It's not exactly like what you have but it will do the job. There are a lot of ways to do what you're trying to do that might look better.
I hooked both of mine up just for shits and giggles. I don't remember where the piece with the ball that I welded on came from. I never used it (not necessary) but it was the only one in the parking lot to have them both hooked up.