Hi Daniel,
that with the elimination of the Arisaema providers from England due to Brexit is actually a pity, some of my best Arisaemas I had from there. Some have stopped trading altogether because they had a large number of interested parties on the continent.
The owner sake Kuijpers is a very serious trader. You've probably already looked at his page. The good thing about him is that he almost always also posts photos of the tubers, so you already know exactly what quality you get. By the way, he also offers on ebay under the name sakepauline, the prices are the same, sometimes he also has arisaemas there, which he does not offer in his shop. I always look at both.
At the moment many of his tubers are already sold out, but he still has e.g. Arisaema wrestling there, which has a fantastic flower.
From his side you can also see which garden markets he will soon be at, since he always has a very large selection with many species of potted Arisaemas, Amorphophallus and others. Most of the time these markets are in Holland (for me that's not so far, for you I don't know).
Otherwise, e.g. Gewieh's flower bulbs (D) and Sarastro (A) offer Arisaemas, but they do not show the tubers.
I myself always look at ebay for Arisaemas, where I have already found something very beautiful with a Japanese (my Arisaema thunbergii ssp. urashima and the variety "Soshin").
And last year our member Michael (musa) started a collective order at a dealer in China, he because of orchids, and I was there because there were quite rare Arisaemas at this provider.
So much for now,
Best regards,
Ada