Hi, this is a topic that I have been looking into in some detail for my vintage Billings Cutty Sark kit.
I considered painting the hull on my model and tested quite a number of paints and there are some that give quite good "metal-like" appearances. However, they do all vary quite a lot in colour/shade/metallic sheen.
I found the metallic brass paints from Humbrol (no.54) and Revel (RV92) were a bit too dark and had a slight "glittery" appearance to them which would be noticeable at the smaller scale. The gold Humbrol paint (no. 16) was probably a bit closer to Muntz but had a slightly more darkish yellow tint to it (again, also a slight glittery finish). Some other "brass" paints were not "terrible" but I did not like the colour/finish they gave so I won't mention them!
The best paints I tested were the ALCLAD2, ALC-109 (polished brass) and ALC-108 (pale gold) <
ALCLAD2 link >. The ALCAD2 paints are designed for airbrushing and I found that they were far superior to anything else - but you do need to follow their recommended painting method to get the best finish. They give an excellent metal like finish and in my tests the pale gold was probably the closest match to Muntz but, that's just my thoughts and you would need to test them yourself to see what you think.
You can see in the image that the brass on the C-S at Greenwich (as restored) is quite a pale greeny/yellow but I am not sure if they used actual Muntz or just a standard brass alloy when they re-sheathed it?
In the end I have opted to sheath the hull on my model in actual brass which I am working on at the moment (but that's another horror story!).
Hope this helps a bit.