Hi racinghero (what sort of name is that?), I recently bought a front and rear tank for my 3AJ from France, its by a company called Motoforms and acording to the seller has been used in the paris dakar and a couple of other desert races.It fits on with the horn being moved and the bottom crossbar mount for the tank being modified to be shorter.
The front tank is really two tanks as theres a divide down the middle and two fillers on top,it fits the fairing and holds 45 litres. The rear tank is really a side and rear tank in one replacing the left hand side panel and tail unit with a filler above the back light, I've not filled it yet but should imagine it takes around 15 litres. Again it fits relatively easily with two rubber mounts in existing holes and the rest of the mounting also on existing holes.
The standard saddle fits (just) and it even came with tenere stickers already on it!
Maybe these are the tanks your thinking about? I came upon these purely by accident but should imagine France,Italy,Spain and Germany would be the places to look because obviously their not made anymore.
Cheers Fish (What sort of name is this!)