Theory is that smokeless power is available to anyone over 18. Problem is some gun shops require that you show your FFTir (french target shooting federation) membership card too.
There's also a 2kg limit (which is the maximum you can store at home at any time) which French gun shops will probably also enforce.
In Strasbourg there's Recht with Vectan and Vithavuori powder.
Luxemburg requires some paperwork before they can sell you powder. They also don't seem to stock that much power (and contrary to ammo, ask you to come and pick up your order as soon as they have it delivered to them).
But if you get through the paperwork and are no bound by stupid restrictions (like our 2kg limit), you could place a large order and pick up a year or a couple years worth of power ...