This will help a little, but not a lot...
The number of Tristars operated in 1994 by Caledonian was less than 19 - I think they had the following in the fleet then.
G BBAE
G BBAF
G BBAH
G BBAI
G BBAJ
So not so many aircraft to chose from.
You don't say where you flew from, but perhaps one of the aviation societies may be able to help.