“Out for Blood,” the new novel by National Enquirer veteran Mike Walker, could give gossip columnists a bad name. The protagonist is an LA-based gossip scribe who happens to moonlight as a blood-thirsty vampire, reports The Post’s Richard Johnson. Walker, who had a No. 1 best-seller with Faye Resnick about her slain friend Nicole Brown Simpson, just signed a deal with Writer’s Coffee Shop Publishing, the Australian firm behind “Fifty Shades of Grey.” “Out for Blood” hits shelves in the fall.