In the FS1 command briefs, it gives you some information on fleet strategy. It refers to four different Orion destroyers (The Galatea, Bastion, Intrepid and Minnow IIRC). Since it only talks about the movements of these four, I assume that during the Great War the GTA had only that many- which implies that Orions are VERY expensive if a entire star race can only build four of them. The only alternate explanation could be that the Shivans/Vasudans destroyed a lot of them (whittled an initial force of, say, 12, down to 4). ST also refers to a GTI destroyer, the Krios, though, so there still could be more out there.
Either way, I get the impression that GTVA production capacity went up a lot between FS1 and FS2 because in FS2 you have all kinds of huge stuff (Collossus and 10km long Aquitaines) even though Earth's industrial capacity, which the game and FSWiki refers to as being considerable, is gone. Maybe the Vasudans helped the GTA a lot in building up their fleet.
