I can see how easy it would have been to jot down (a) and also how mortified you must have been to return to it upon rereading. See this question for some background on a curious and related matter that applies here.
The gist of it is that some folks think that pronoun coming after the preposition that separates it off from the main subject sounds better as a subject pronoun to them, not as the object of a preposition.
It is if they were letting the preposition act not like a preposition at all but like a coordinating conjunction (well, disjunctively) instead and so not affect the case at all: it keeps the subject case for them.
This leads to things like
Nobody but I am going to tell you.
Nobody but me is going to tell you.
As for your myself version in (b), sure, there are places where myself gets used emphatically other than simple subject–object reflexivity, and arguments might be made for that route. You could perhaps get away with doubling up here:
I’m surprised anybody but me myself had a cat named Hamlet.
But I really think you will do better going with your (c) version in the long run. It’s simpler, and hard to disagree with.
Still, you should say whatever you like. It’s your language.