I am working on restoring a 1972 Plymouth satellite sebring plus. It has the two tone paint scheme. it calls for dx8555 for the lower silver thats from body line trim down. This seems to have not been available for decades. Is there any know substitute for this paint?

Here's a few links for you to check out.

https://www.mopar1.us/argent.html

http://www.dodgecharger.com/forum/index.php?topic=114367.0

https://pantera.infopop.cc/topic/correct-paint-color-for-stock-rims

i would suggest stopping by a PPG paint store or a PPG certified body shop.
have them use their color camera on the color. this will give you some paint codes with match ratings #'s. the lower the # the better.
then check the color variance deck for spray out samples on the code referenced by the camera.
you should be able to get a modern color that's pretty close to the original color this way.

I would go with PPG 32398 per paint ref.

Link 1
Link 2

I would get a 4oz sample locally and do a sprayout. Check it out in different lighting, validate it.

Check with TCP Global and see if the can mix it for you. Pretty sure they can. Link

my brother had one of those in the exact color scheme around the 1977-1980 time period ! it was a 400/727 combo with a slapstick shifter.
he "borrowed" a few wheel and tire combos from me, changing them out when the rear tires "wouldn't pass state inspection".
boy, did he ever beat on that thing ! good thing i owned a junkyard during his ownership........