Chris,
My good friend @ed h is spot-on with his response.
The Service Station sets from 1971-1976 were announced with a Service Bulletin page as shown above. There was also an order form, but photographs or illustrations weren't ever published by Lionel. The sets relied heavily on items in the regular line (1971-1972) or postwar reissues (1973-1976), so perhaps it was thought that imagery wasn't necessary.
The 1977 Service Station set with the Budd Cars does have a one-page "sell sheet" consisting of line art. Then a full-color sheet was issued for the 1978 Minneapolis & St. Louis set. Full-color sheets were also used for the service station sets when they started again in 1986.
Hope this helps.
TRW