Seems the LC had a factory for at least most of the unseen designs and many of the TRO3039 designs, including downgraded 2750 mechs.
However I agree with previous posters, by 3025, you are just as likely to find DCMS or FWL salvage, like Awesomes, Dragons, Jenners, Hermes, etc. By 3039 you would start to see designs like the Victor, Enforcer, and Valkyrie, from the Davions. By the 3050's the Fedcom had fought everyone, there is a good chance to justify any mech being fielded by the Lyrans.