I don't know why you need to model a transmision line. If you correctly terminate the line with a resistive load equal to its characteristic impedance, then you will get out of its end the waveform you put into it. The input of the cable will then look resistive and if you like you can add series resistors as Ron said, but those will only attenuate the signal.
That said, any transmission line has an attenuation that increases with increasing frequency, and that will affect the amplitude of the signal at the end.
If you look up the manufacturer's data on the transmission cable, you will get its characteristic impedance, capacitance and attenuation per unit length and, in the case of RF coax, its velocity factor.