I don't believe K-line ever produced these as 21" cars. They appear as 18" cars in the 2006 Vol 2 catalogue as one 4 pack and two 2 packs.
K-4681D 3006 Obs, 31186 Diner, 32015 Coach, 31562 Baggage
K-4681E 32002 Grill, 32060 Coach
K-4681F 30593 Combine, 32050 Wall Street Club
They are all difficult to find, but I looked for 9 years before I found the club car.
It's best to consider upgrading them to LEDs, because they have high current draw, flicker a lot, and had poor quality control on the wiring. I found dead shorts, disconnected wiring, and bad rollers. Having said that, they are magnificent to see running behind the matching K-line F units; especially after I got a smoking B unit from bluelinec4 (Ben).
Next up they go for a Ramble behind the new Reading T1.
There is a guy who specializes in K line passenger trains; he claims to have a room full of boxes he can't even access. I'll try to contact him and put him onto this thread.