Your best bet would be to contact Soudetam and ask about their Fastin flux, I don't know of any reseller in France with a web shop, maybe they do. That stuff is already hard to come by over here, some of the shops I know will want to sell only to pros and I'm pretty sure won't ship but deliver locally only... Heck they still work with a fax to take orders.
That's the stuff: http://www.soudetam.com/anglais/structure0.html Here is a pic Fastin from the above link:
Old thread, but here is video proof that you can lead aluminum using 30/70 and NO tinning compound. Got a kick out of reading this thread and nearly everyone saying it's impossible.