Hot Peppers

Some UK vendors:

• Sea Spring Seeds - these people have single handedly kick started development of super hots when they created Dorset Naga. A trully obsessed chilli heads, selling seeds since 1994, their selection is kind of limited, but the quality of their seeds is undisputed.
• South Devon Chilli Farm - another long standing chilli farm. Their primary focus has always been chilli sauces and condiments, but they also sell a variety of seeds. Again - excellent quality!
• Suttons - this is a very old horticultural establishment, almost as old as US :) They sell all kinds of seeds, seedlings and equipment, including chilli seeds. Their chilli selection is very limited, but they have some rare (in the UK) seeds.

Note that some of the vendors listed here are controversial. Certainly there are a couple that I listed where I personally would never buy from them, but that's more for personal/ethical reasons. They all, in my opinion, are vendors who will give you what you paid for (accounting for unstable varieties, cross pollination, and the occasional honest mistake) despite any other criticisms.

For EU :
https://www.semillas.de/
https://vertiloom.be

I’ll give +1 to white hot peppers! Everything grew true to what I bought.

For anyone in the US who wants New Mexico "Hatch" chiles Sandia Seed is decent.

Native Seeds Search in the U.S. has some interesting varieties, and the seeds are good quality in my experience.

https://www.nativeseeds.org/

All, except 2, EU links are from the UK. :)