A 59 DeSoto conv. was used almost a star itself in Mystery Date with Ethan Hawke & Teri Polo (1991).

is there a way to add a car here for inclusion to this site?

Sure, all (or nearly) what is posted on this "contributions" section will be added as soon as possible to the site by the admins (usually by me, Garco, and few others).
You can also post pictures here using www.imageshack.us (copy/paste the link "thumbnail for forums (1)" on the result page)
When the info is added to the site the thread title is changed to add a "[done]" tag in the title.

btw I added the car: http://www.imcdb.org/vehicle.php?id=51412