What's the big mystery? They were made by Display Systems, a little company run by the late Ev Penn in the L.A. area.
I had a conversation with Ev shortly before he passed away around 1981. He helped rebuild the Concentration game board and controller when it was shipped from NY to LA. He and Ted Cooper redesigned the controller because on the one used at NBC, "the operator had too much to do". When Ev passed away, I'm told his wife made the readouts used on the second run of Tattletales. I built some readouts using IC's and ROM chips but never got around to designing a diode matrix which would pretty much require a printed circuit board.
The "egg crate" was made of polyurethane impregnated with aluminum powder to make it silver. The holes are 5/8" in diameter. It used 1820 lamps which were very, very bright and gave off a lot of heat. The heat from the lamps used to cause the holes in the polyurethane to deform and come out of round. But they were dependable and simple to drive. Display systems also made a larger dot matrix readout and a seven-segment display which was used on bidders' row and also on Card Sharks. Ron Schwab of Vista Electronics designed his own line of these readouts with square holes and an "egg crate" made of metal. They were used on "Debt".
Nowadays if you wanted that character set you would use a 16x9 monitor and do it all in software. If you just had to have a replica of the Display Systems readouts you could copy the same basic design but use LED's, which are expensive.
Don't forget, Card Sharks had readouts that spelled "BUST".
Display Systems was based in L.A. In New York they used readouts made by American Totalizator for TPIR and Say When!!
With these lamp matrix readouts, you could put them behind a sheet of scrim, paint the scrim any color you wanted and let the light shine through (scrim is a loosely-woven fabric). This was done on the contestant desks on the CBS version of Match Game — one red and one green.