How to find a saturation current for BJT from datasheet?
The easiest way to find reasonable numbers for the Ebers-Moll parameters is to look at existing SPICE models. 

For example, the BC856 ISC = 1.633E-14 (NXP model). 

ISC is base-collector saturation current. 

There's also IS transport saturation current and ISE base-emitter leakage saturation current. 

Deriving a reasonably accurate model from a BJT datasheet is non-trivial. You can find a quite lengthy description here.