I can't think of any campsites around there, and I walk in that area quite a lot. I know of people who have camped near the pub in Hesket-new-Market, the Crown, in a semi-official way. It might be worth ringing the pub to ask about this. Another option would be to stay at Skiddaw House, which is an independent hostel affiliated to the YHA. Great location and run by a very friendly couple.