Arduino Leonardo - Using ICSP pins for serial
From packages/arduino/hardware/avr/1.6.*/variants/leonardo/pins_arduino.h:


// Map SPI port to 'new' pins D14..D17
#define PIN_SPI_SS    (17)
#define PIN_SPI_MOSI  (16)
#define PIN_SPI_MISO  (14)
#define PIN_SPI_SCK   (15)

static const uint8_t SS   = PIN_SPI_SS;
static const uint8_t MOSI = PIN_SPI_MOSI;
static const uint8_t MISO = PIN_SPI_MISO;
static const uint8_t SCK  = PIN_SPI_SCK;



Those are the pin names and numbers you can use. Note that SS/17 is connected to the RX LED.