Customers of Barnes & Noble and Borders are complaining that the anti-John Kerry book “Unfit for Command,” has been hard to find in the stores. And they’re charging the stores with political bias against the book. The stores say they just haven’t been able to keep up with demands. The book, which went on sale Aug. 11 with a first printing of 85,000, will have 550,000 copies in print by next week, according to Regnery Publishing.