A fascinating thread, which I've been reading since it began.
I don't know of a Breguet 14, other than the old 'Aurora' kit in 1/48, or the more recent 'Hi-Tech' one. They turn up on e-bay sometimes.
Force of Arms do some French trucks for the Spanish Civil War period, which you might be able to pick up from
Wargames Command Post, if they are not too late for you to use.
Sloppy Jalopy do some Ford trucks. Not perfect solutions I would imagine, but possibly useful.
Looking forward to future instalments!