All the older Fiats I've worked on seemed to have the same toolkit in a plastic box.
These toolkits are often advertised on Ebay under e.g. Classic Fiat Tools.
(at sometimes exhorbitant prices!).
Just mentioning this as you might find what you're looking for from a different model Fiat. Some other members are I'm sure experts on the 126 bis and can advise you if the above is true or not. Some might even have a spare toolkit to help you out!
The tools I remember are:-
8 x 10 mm open end spanner
13 x 17 mm open end spanner
8 x 10 mm box spanner with built in T bar
21mm plug spanner
Tapered drift/bar to turn plug spanner
Wheelbrace 19mm, 'L' shaped with screwdriver end to remove hubcaps
Screwdriver with reversible blade, straight slot + No.2 Philips (screwdriver handle was wooden on older models, black plastic on later models)
All the above fitted into a grey plastic box.
Vehicle jack was usually a pillar type with a side arm which fitted into a jacking tube just under the sill. The length/height of these jacks varied a little between models. Some other models e.g. 124 coupe used a Scissors type jack in a (front or rear) jacking point under the sill.
I'd be interested to hear if I've omitted anything or if anyone has encountered anything different with older Fiat models.
Al.