Blood of Kerensky Trilogy is where I would start by Michael A. Stackpole. I find many paperback copies of this in used and half price bookstores nearby.
From Wikipedia........
Blood of Kerensky Trilogy
* 1989 Lethal Heritage (FASA)
* 1990 Blood Legacy (FASA)
* 1991 Lost Destiny (FASA)
There are many battletech books that came before this, and they cover a timeline before the Clan invasion. If you want relevant materials to what this game portrays, start with these three and then follow the timeline list found here :
http://en.wikipedia.org/wiki/List_of_BattleTech_novels