This year there is a drumlanrig event with a 100km+ option.
http://www.mtb-marathon.co.uk/events/3rd-august-2014-drumlanrig-castle-scottish-borders.html
Anyone fancy it- 3/8/14 £30:00 entry.
Would enjoy giving something like this a go, I'll be off work then as well.
Hoping to get back on bike this weekend so give it a couple of months of riding to see if I can say Yes.
Mark