I tried Ford blue engine paint (which a local store carries). It's a bit lighter than Miller blue. Today I went to Grainger and they carry Rustoleum Industrial Enamel in Deep Blue, and it's real close. It's close enough to use it as touch-up next to factory paint, and you have to look real close to spot the line. The label says "V2125" and it's Grainger item no. 2FP62.
It's expensive, but the cans are 12 oz not 8 and the one I've shot so far sprayed real good until it was empty.