As the title says, I am looking for a mix that would replicate the off-white interior color of a King Tiger using Tamiya paints (the arylic line.) I have searched the webs, but came to naught.

Hey Brett, look for a thread in here titled WW2 German AFV camo datasheet/timeline by Matt Toms, I asked the same sort of question and its all very informative, lots of great info ... John

This is the color I used on my Trumpeter 1/16 Panzer IV interior, made up by myself, using Tamiya acrylics.

Keep in mind the color should not be "Elfenbein" or ivory.

(Taken from sources on 'net):

For the first part of the war, and probably before the war, the official paint scheme for tank crew compartments mandated that the red primer be completely overpainted. There were two colours used; a yellow colour called Elfenbein (Ivory) for the upper part of the compartment, and a grey-green colour for the lower part.

Elfenbein was RAL 1001, which is a light lemon yellow colour. However, we have found only one vehicle which seems to have had this colour inside, a Panzer 4 from early 1941. Although no record of a change has yet been found, it seems that the interior colour was changed to a light beige after that time. Several vehicles have been found with similar beige colours inside, and the Panzer 4 mentioned above was repainted beige, probably when it was upgunned.

The grey-green colour was RAL 7009. Mr. Doyle had the opportunity to compare some of this, on the Bovington Tiger, directly to the wartime RAL colour reference card: even after 50 years it was extremely similar.

My Formula for the mystery "beige" interior color of German armor:

20 drops white
4 drops buff
4 drops deck tan
1 drop yellow.