found a company that has van door seals, mine is a 78 b100
they have 71-77 Will they work on my 78?

According to some of the NOS Parts suppliers list the same seal fitting up until 81 model year if you're referring to the front doors only.

No, it more like the back doors and side doors.

You can also check restorationspecialties.com - in their catalog they have a bunch of different seals.
Much is by the foot, but that might help you.
Years ago I called them about window channel felts for my '63, thinking it was a certain measurement.
The guy there corrected me, and he was right !

In that case when I looked up the part numbers I didn't see any for 71-77 but, did see it goes up to 84/85.