I used to get most of mine from Everit at the Guildford show, they were apparently Swiss made but I don’t think he is trading now.
EKP would be my next choice and they make the ones several of our other suppliers sell. Not bought much BA lately but I did find their 8BA nuts were not as nice as the other sizes.
Also with all suppliers now that BA hex is getting harder to find you may get a close metric or imperial size rather than true BA so check if that is important to you.