Thanks, Steve T and Maeve - the "Guest" with a sigh above was of course me sans cookie.
I'm working on this romance for a PhD thesis, part of which will be to see what happens to an old story when told to a modern audience and part of which is attempting to come up with some answers to some of the problems found within it. I know that I will not get away with any fudging, which is why I'm looking for references and solid information rather than hunches - and I know that there are Mudcatters who are excellent at furnishing solid references when they can! So please, by all means contact any other experts who might be able to point me at other references and I apologise for sounding ungracious earlier!
In the context and in the absence of any other references to Avalon it seems unlikely that Kay's baton was a sign that he was from there. And yes, there are boughs with different bells on for bardic authority, but Kay is not a bard and there are no bells on his baton.
Thank you all for trying!