Yes, you can get flannel sheets for your king bed as long as they are in the king bed size. You can find some bedding at stores like Wal Mart, Target, K Mart, and Overstock.
You can get bed sheets for a king size bed at any store that sells home decor. You can try Bed Bath& Beyond, Walmart, Target, or Sears. You can also try online if you can't find anything you like...