Dear shaq,
I think a very easy way would be to design a very simple circuit with an NMOS device and the run it. Take a look at its output file (e.g. .lis file in HSPICE) to find the value of its beta, which is
beta = µnCox * (W/L)
so by having the value of aspect ratio, W/L, you can easily find µnCox.
But another not very good way is to fing the value of "u0", which is often a good approximation of µn, times the value of Cox, which is calculated as εox/tox.
However, if you use the first way, you will find out that this value changes a lot for different situations.
Regards,
EZT