Some auto parts stores that mix paint can do smaller custom amounts, even spray cans. I have seen some on ebay but I don't know how close the match is. Also, some of the Turquoise and Aqua paints from NPD listed as interior paint can be used, even mixed in a plastic cup then dabbed on.
if you have the paint code, NPD might have what you need, or can get it. if you have a sample, ie paint chip or something similar, you can have a local paint shop whip some up for you. you can also contact companies like PPG, house of color, and other automotive paint manufacturers and see if they have the blend codes to whip up a batch for you.
Try Googling " 66 mustang tahoe turquoise spray paint". That's how I found mine. The spray cans are expensive but appear to match the original (couldn't be positive as the PO covered most the exterior with grey primer).
I went to my local paint supplier. I replaced my original trap door with one that had already been cut for speaker holes when I installed my sound system as I didn't want to cut up my original. I brought the original trap door in to them and they were able to mix up a couple spray cans for me by matching the trap door paint.
I know you already ordered, but the best way to do this is to have your actual paint scanned at the paint store. The scan will generate a paint mix to match your paint and they can then mix and load it into a rattle can for you. Most larger paint stores have the ability to scan, or can put you in contact with one that can.