My take on the Gotha and Stingray point. By checking the MUL i can only infer what the MUL team was thinking.
The Gotha was made by Allied Technologies of Stewart until they got conquered by the Wolves, and the line was reporpuse for the Goth ASF. The -400 and -500 are in the MH lists, until the DA era when both appeared only in MH (and pirate in the -400 case). Checking more modern variants, they are still avaible among the FWL states. My theory is that both the -400 and -500 were sold in the free market, with the FWL prefering the more modern variants, and the Hegemony using the oldest because of a logistical issue. The thing about the ASF in the free market are supported by the Stingray -94 and Lancer LX-2, both made by the same producer (Gutierrez Aerospace), until the factory (Trellisane) got conquered by the Wolves.
Now, checking the Mechs, and in lesser importance, the combat vehicle, list, there is a notorious predominance of FWL and LC models in the MH list, with the more "new" mechs beign Lyran against the more "clan invasion" models of the FWL origin. Another example is the Marsden MBT II-A (LB-X). There are a number of mechs and tanks that appears in LC, Merc and Marian lists, but no other place.
As you said, dropship collar is the bottleneck of interstellar trade, and i agree that sending a "empty" JS to the LC just to get mechs would be criminal, but the LC was, and still is, a merchant realm, with organizations like the Lyran Free Traders Association having like 200 JS going around the LC, its neighboors and even the Periphery, or Nashan Shipping, to mention some.
And even with their reduced JP production capacity reduced (bye bye Alarion, you will be missed), Germanium, as other minerals as cobalt, or even the Alphard White Marble could be exported back to the LC.
If you check the books, all, even in the dark ages of 3025 trade was still active trough the Inner Sphere and the Periphery, and even in far places like New Syrtis, people could get Timbiqui Dark.
So, while i usually differ with Adaca about the Marian hegemony´s capacity to produce this or that, i have to support him in the theory that the Marian Hegemony have some kind of trade relation with the Lyran Commonwealth, based in the mechs and vehicles avaible in the MUL.