Bonjour Olivier,
Bienvenue sur le Forum.
There are lots of Diablos for sale in Europe.
I would suggest you get in touch with Fabrice (Fab1 on this forum) in France. He is your best chance to be introduced to the right places and people to help you find your Diablo. I don't think there are much in France though..but if you really are ready, you will find many in Germany or Switzerland. Get ready for some endless hassle with all kinds of administrations to bring the car back in France...suspicion, jealousy and resentful...Expensive exotic cars are not welcome in France...or is it the people who can afford them ?
Not being a genious Mechanic is fine. You just need to know the basics, and that's all you'll be able to do anyway without lots of equipment or tools. I know the best Mechanic in Europe in Switzerland. We would fix any engine at a reasonnable price. He completely rebuilt my engine and gearbox (see the Tahiti saga if you are interested) and has rebuilt a few Diablo engines as well. Let me know if you need his contact.
Be aware that "Reasonnable price" still means a lot of money. These cars need a lot of care...
Voili voilou...all for now.
A+