I'm not sure if anyone else noticed, but it looks to me like the brass weight is still in the carb body in the picture posted by Mako21. I seem to have lost the check ball brass weight from my Holley 1945 this last weekend as well.
I rebuilt my carb this weekend, and didn't realize I had lost the brass weight until after I had started the Dart and set idle. It actually ran better than it has since I bought the car. Then I pulled the distributor to replace the vacuum advance solenoid. Got that back together an installed and it started right up, set timing and it ran great. Drove it a few miles with no issues. Then last night I noticed a little ball bearing on the garage floor. I knew the carb kit had one in it, but there are usually parts in carb kits that aren't used on a particular vintage, so I didn't worry about it.
Well, I never did find the brass weight. I am also having trouble finding a replacement online. I did find some dimensions online, so I will likely try making a replacement. Googling around, I saw in another forum where they were saying that if you don't install the ball and weight, that the accelerator pump won't work. Well, it obviously works without it as I was driving around without it. Anyone have a little more knowledge than I on the actual operation of the check ball that can make sense of what occurs without these parts? Any ideas on where to purchase replacements? Can I replace the ball/weight combo with the conical shaped weight style? They seem to be more readily available.