The name space of these dealership codes is enormous, spanning 5000 - 68999, with the range 10000-24999 possibly not in use for US dealerships in the period we are interested in.
Some examples:
05475 Sternberg Chrysler Center, Inc., Jasper, IN. Incorporated September 19, 1952
25047 Deloach Dodge, Inc., Monroe, LA. Incorporated September 28, 1967
37516 L.P. Steuart Silver Springs, Inc., Silver Springs, MD. Incorporated April 12, 1939
39659 Pepper Auto Sales, Inc., Syracuse, NY. Incorporated July 22, 1958
65833 Huff Chrysler-Plymouth, Inc., Boone, NC. Incorporated May 12, 1976
68923 Swaffer's Gateway Chrysler, Inc., Clare, MI. Founded 1971
And from outside the assumed available name space:
12003 Chrysler Corporation Fleet Division Employee Lease, Detroit, MI
13715 Alberic Dodge Chrysler Corp., San Juan, Puerto Rico
69907 Feeny CP/Citicapital Leasing, 2312 Trinity Mills Rd, Carrollton, TX
90041 Chrysler Motors Corporation, Cincinnati, OH
That makes theoretically for 64,000 - 15,000 = 49,000 codes out there. For a comparison with this outcome, it would be nice to know the maximum number of ChryCo dealerships at any single point in time. Still, any heroic attempt at getting the codes together in one place is likely bound to fail.