If your looking at finding a box at a scrap yard, the Porsche and ZF options I believe are out, nearly all Porsches are dismantled and the box hardly touches the floor as they are quite sought after.
One exception may be the Boxster Gearbox, not used that much by builders and handling 250 maybe 300bhp, also all setup the right way round no flipping the box etc.
The other box you might keep an eye out for is the Audi A6 2.5 TD box this and a few other Audi variants are as good as you get from Audi, some state good for 350Bhp.
Some Renault boxes still turn up, the car your looking for is the Renault 21 Turbo, but some Renault 25's had a good box as well, lots of mods for the renault Box.
Lastly the Lotus Esprit gearbox, based on the Renault, but with some mods.
Happy Hunting