There is an ADV in local Craigslist type of site here in France, for a 92 liter tank since some time. The person looks like he has several tanks. He is asking for 500 euros, but I am sure he will take way south of the price. Here is the link,
If you encounter any problem or your communication fails with the seller, maybe I could help...
Reservoir essence porsche 993 964 996 986 Equipement Auto Nord - leboncoin.fr