That we know? The Primitive Emperor, but as the actual productive capacity of the Marians is at best "nebulous", we can infere, taking in count things like the last Withworth fluff, that the Marians are using newer models. The Tamarind are much ahead of the Marians, the Tamarind local productive capacity is not that big, and even with their recent (for the timeline) rejoining with the rest of the FWL, it would take some time to replace and resupply all the units.
As for what Ark says, its something common with the chosen line by TPTB for the Marians, beign the "evil orc" for the FWL/MoC or any other faction. I miss when BT was more grey...
Amen!
If we go by Withworth's fluff and only that, the Hegemony or rather Marian Arms manufactures 4 medium mechs (Centurion, Withworth, Icarus II and Gladiator) and 1 Assault (Emperor) after having passed all their primitive lines first to Succession Wars technology and then at the end of the decade of the 3130 SL level.
The ATC has been making Commandos and Locust for a long time, at least since 3085, manufacturing all its components locally, we don't know anything else about them, maybe they build some more mechs in Addhara but nothing came out in the Rec Guide so keep waiting
Nothing is known about Hadrian Inc or the Techwizards, so about them as well as ATC Addhara we will have to keep waiting (if the J E Hoover of Addhara came out and what was produced in ATC - Illyria) the rest will have to wait