Jason,
That is simply pathetic. They'll cover someone hurtling down a mountain on a piece of wood, but not running!? People die doing all sorts of things - is that not part of the purpose of insurance for Christ's sake!?
I can't suggest any companies who might be able to help I'm afraid, but I'd be interested to know who the company is that declined you insurance when I see you next.
BTW, have you got your accommodation and travel to Dublin sorted yet? Also, I had an email from Amazon yesterday saying that after about 3 months of searching they can't obtain a copy of 26.2!!!