Depending on what type of MOSFET you are needing and what your voltage levels are will determine what kind of model parameters you will be needing. For instance, if it is for large voltages (>5 V) you will be needing a different type of MOS with different parameters than one which is less than 5 V.
I don't know much about higher voltage FETs, but for <5 V applications an okay place to start is through the MOSIS web site (www.mosis.org
). They keep a detailed list of SPICE parameters for different size technologies (from 1.2um CMOS down to 90nm) with different runs so that you can see the process variations. As far as needing an ft of greater than 20 GHz, you will need to use at least 0.35um CMOS. Even then, it may be pushing the limits.
If you can't find the information you need on the MOSIS site, you can always check foundry web sites. Sometimes they post their SPICE parameters there for older processes and you can see if they are in the ballpark that you are in.
Hope this helps.