Names of the letters

I had an obsessive compulsive moment this morning and decided I needed to know how to spell the names of the letters of the alphabet. Isn't it odd? We sing the names of the letters of the alphabet from our earliest years, but we rarely write them out. Most writers when they need to do this simply use capital letters followed by an apostrophe, e.g., "Mind your P's and Q's." That is an abomination: the apostrophe should be reserved for possessives and contractions, not lazy plurals. So here are the spellings I've tracked down. I'm most dissatisfied with the spelling of a and ex. I think we should spell the former "ay" with plural "ays", and the latter "eks" with plural "ekses", but I couldn't find any justification for that in current dictionaries. I'm going to spell them that way in my own writing anyway.