Hi Kent - First, to answer your question directly, I've had good luck buying from these guys.
https://www.pegasusautoracing.com/productselection.asp?Product=1580 I'm not sure you need a kit if you already have a set of these in your car, so I just linked to the carbs themselves,
That said, a rebuild would be much less expensive, and I would recommend that. There is a guy here in SC who all the local muscle car guys use. He calls himself "the carburetor whisperer", but he's not a Weber specific person. That said, I've met him a few times and he knows his stuff. I could hook you up with him if you want to go that route.
Another comment: I had a pair of these on my car before I changed to the triple DCOEs. In talking to Carl Nelson about these carbs, he told me that he prefers the 38/38 when he does a Weber swap. If I remember right, he specifically preferred the mid-range performance. If you are going down the replacement path, I suggest you look into the 38/38s.
As to installation tips, take the time to go over every inch of your linkage. Make sure the bell crank bushing is in good shape, moves freely without any wobble and that the spring is intact. Check that the stop on the bell crank is in place. Make sure your accelerator pedal is in good shape, with particular emphasis on the junction at the top where the rod goes through. Mine was broken off when I bought my car. Then check each ball end on the rods within your linkage to make sure that they are not corroded and lubricate them so they move smoothly. Mine cleaned up nicely with some steel wool and WD40.
Also, consider replacing the hose that goes to your vacuum booster along with the check valve. These are inexpensive and replacement should help ensure you don't have vacuum leaks.
