It's an event I've been interested in for some time too, since reading a souvenir book from Carrickfergus castle, though I can't be much help about it: that and a couple of other local history books only really mention Edward Bruce in passing.
Amazon throws up a couple of titles that might be of use. I'll probably have a look at one or two of them myself. In the meantime, I
think kern at the time might've been more like those that Corvus Belli sell for their
HYW range (pity they're 15mm) - which seems to have been a look kept through to the
15th and
16th centuries, relatively unchanged. Dark age irish with bare legs rather than bare chests might be fine at a pinch.
But don't quote me.
(Ebob had a nice gallowglass sculpt up on his
forum, for his Rebellion range, with promises of a kern soon after, which would've been perfect. But that was years ago and AFAIK neither materialised in his webshop.
)