Charge carrier density for alloys

If we go to Aschcroft&Mermin we find formula for charge carrier density:

$n=frac{N_AZrho_m}{m_a}$

This formula is pretty simple and written in every solid state physics textbook.
So my question is: Is there a formula which allows to calculate charge carrier density for a specific alloy? For example, it is possible to calculate $n$ for Sn and Pb elements, if we melt them together we will get most common solder alloy SnPb, but is it possible to calculate $n$ for SnPb? (And any other alloys?)

References to textbooks would be much appreciated.