You want a copy of the Twenty Year Update
, I think. I don't know how detailed it is about the FedCom ORBAT, but there's definitely something in there. If you want something that's still in print, take a look at Era Report: 3052
- ostensibly post-clan invasion, but intended for play during it.
EDIT - according to FM: Lyran Alliance
, the 3rd Lyran Guards led the capture of Alphecca in 3044 and were redeployed to Graceland during the Clan invasion. There's no mention of anything in between, so I'd assume they garrisoned Alphecca in the interim.
Edited by Karel Spaten, 03 April 2012 - 07:25 AM.