The main reason for that is because PIC16F913 doesn't have MSSP(master synchronous serial port) but instead has SSP(synchornous serial port).
An MSSP adds logic to act as a Master I2C device. An SSP can only act as a slave, you have to "bit-bang" to act as a master.
Additionally, the SSP-module doesn't support the General-Call-Address (slave-mode), which the MSSP-module supports.
That's the reason why there is no library.
As I mentioned before, you would have to "bit-bang".
Bit banging is a technique for serial communications using software instead of dedicated hardware.
Software directly sets and samples the state of pins on the microcontroller, and is responsible for all parameters of the signal: timing, levels, synchronization, etc.
In contrast to bit banging, dedicated hardware (such as a modem, UART, or shift register) handles these parameters and provides a (buffered) data interface in other systems, so software is not required to perform signal demodulation.
Bit banging can be implemented at very low cost, and is used in, for example, embedded systems.