Ron, as you already know, there have been several different formulations for MID over the years. Some are more pearlescent than others, but all are a combination of blue, red, black, yellow, and pearl toners.
Using a hobby enamel paint set, and combining the colors mentioned above, would give a very close approximation of any MID shade. In place of the pearlescent toner, you can add tiny quantities of the silver enamel until you've reached a color of just the right shade and degree of pearl (or metallic) quality.
I'd start with blue, adding a bit of silver, and then darkening it with a bit of black at a time. It will help if you blend these in a small bottle with a cap, so you can keep the extra for future touch-ups on the same instrument. If the finished color seems too purplish, add a touch of yellow. If it seems too greenish or turquoise, add a touch of red.
Roughly the same rules would apply for nail polish (which is lacquer), although you'd look far and wide for bottles of these shades that were pure enough in the color spectrum, to allow them to be mixed without muddying. This is especially true of the blue and yellow. Pearl is easily found in lacquer nail polish shades, but difficult to find in hobby enamels.
Testors' makes a kit for about $12.00 that gives you everything you need for this. Toss the brush, though...it's junk for any kind of precision work like chip touch-up.
http://www.hobbymasters.com/index.asp?P ... ProdID=538