There is always the option of ordering from within the EU, not quite tax-free because Brexit, but maybe a little cheaper.
Metaluna, in Paris, they have a lot of the Severin catalog:
https://metalunastore.fr/collections/severin-films
Also other publisshers:
https://metalunastore.fr/collections
I've ordered from them several times already and there was never any problem, even occasionally accomodating more unusual shipments.