We managed to sort-of replicate some optical tags for a repainted pair of "L" cars last year. The tags in question are not the ACI KarTrak type; instead, they're tags from a similar (but not identical) bar code system which was produced by Wabco. I'm not an expert on ACI tags, etc., but as I understand it, this Wabco bar code system was one of four which the AAR tested prior to selecting a system of automated car identification. Although KartTrak was chosen there, the Wabco system was used on (at least) the CTA.
For the tags on our "L" cars, we were fortunate enough to have been donated (by the CTA) a stack of surplus adhesive Wabco tags which were printed printed for a multitude of cars in the same series but never used. One of our volunteers did the necessary homework, and deciphered the bar code. Then from the stack of surplus tags we had, he was able to cut (very carefully) the correct bars for each numeral corresponding to the numbers on our cars and affixed them to a "base" tag. The end result is an accurate bar code which looks pretty good. (see photos below)
The tags themselves seem to be made from reflective Scotchlite, and I've been told by the volunteer who did the legwork on these Wabco tags that proper ACI KarTrak tags are comprised of the same material. An X-acto knife, straight edge, and a supply of Scotchlite in the right colors is probably all you need to make new ones.
The tag is on the first side door from the front of the car(s), in the green area below the windows.
Closer shot of one of the tags, taken the other day (in so-so lighting) in the barn.
Up-close, you can see how this tag was put together using the individual numeral bar codes from the supply of complete tags we had on hand.
Wabco logo