there are a few charity challenge based ones, most of which are eye wateringly expensive and take a serious amount of effort fundraising. (deloitte, action medical)
I suggest that you organise it yourselves and set up your own just giving page if you want to.
Pay for the CTC lejog pack and do the ‘B&B’ route in there
work out dates and book b&B’s each night (suggestions in the CTC pack)
pack very light (carradice saddle bags are bollox though!)
Do it south to north for the wind direction
use ‘john o groats bike transport at the far end (we flew back while he posted our bikes for us)
I did it in may this year, 4 of us riding, 9 days, 1000 miles total and it was great (we were v lucky with the weather, it would be brutal if you wernt!) feel free to drop me an email 🙂
The key point is the CTC pack and johnogroats bike transport both make it simple enough that you can organise it yourself in a day or so
See my posts from before I went http://singletrackworld.com/forum/topic/lejogjogle-advice-please
Dammit amit of this parish also did v similar
https://skydrive.live.com/redir?resid=A5B2FA297AA35578!6415&authkey=!AObE1C2gYpFJ7e0