Finally found one: https://meaningcrafters.com/produit/powerbank-alex/
I don't speak French but placing the order was quite straightforward. Shipping costs were a bit high, but totally worth it. ~~Highly recommended!~~
Edit: Probably too good to be true, see discussion below...
Sooo. The subcontractors in China are all in the greater Guangzhou area? ๐ฌ
I really want this thing to be locally manufactured, but the electronics and battery will most probably come from Asia anyway...