Xewki,
I know absolutely nothing about Cacti, but I do regularly buy succulent seed from CactusStore, who are based in Phoenix USA.
I just had a glance and they have Aureas/ Magnificus / Pachycladus seed all at 25 for $1.50. I pay about $5.00 postage to France, and I would expect delivery within a month.
I've used them, amongst other suppliers for a couple of years. The seed is usually quite good, with app. 60-70% germination for my
Agave and Aloes. However, if you did try them and they were no good .... please don't blame me!
All the best