Hi Daniel
If you want to blue your own screws – which you will probably have to – you will have to find plain steel screws ie. non stainless/ zinc plated. This can be tricky.
If you are looking for cheesehead, by far the best steel BA screws I've found are from Macc Models.
I recently had to polish and blue around 40 12BA screws. It really didn't take that long. Although not quite watchmakers quality, I'm very pleased with the result. I have to do another 40 soon.
How many screws do you need to do?
If you're interested, I can tell you how I did it and maybe post some photos.
Cheers
Steve