IMHO, the best bet is to get your parts re-zinc plated. It is really relatively inexpensive ? as long as you have a quantity. Most zinc platers I know about charge by weight (100 lbs or thereabouts), or by the 5 gallon bucket full (about $120-$150). That?s a lot of fasteners in a 5 gallon bucket. Your solution is to find someone who is going to get a lot of parts zinc plated, and ?piggy-back? on theirs.
If you?re not doing concourse, get out of here ! (just kidding). This might be an option ; about 15 years ago, a 30+ year Restorer of 1955-57 Thunderbirds, told me that, if not doing a ?full-bore? concourse restoration, he uses Krylon Dull Aluminum Metallic (1403) to simulate cad and dull zinc finishes. To end up with a bright (shiny) simulated zinc finish, you may want to try either spraying a gloss coat over the Dull Aluminum, or possibly try the Krylon Chrome Aluminum Metallic (1404). I have not tried either.
For your information, and viewing pleasure, I have attached pictures of an original carburetor stud that I just cleaned and painted (to give you an idea) next to a bright zinc plated NOS one (on the right).
I too had tried all of the Eastwood varieties, as well as Krylon Stainless, Nickel, etc. to try to simulate not bright zinc, but dull zinc and cad, and found that this 1403 was the closest.
Bottom line, being as you just had your car painted, I would have the parts re-plated. Compared to the cost of your paint job, the re-plating would be just ?a drop in the bucket? (pun intended).
Hope this helps, and if nothing else, gets you thinking of the options.
Bob