Okay so I found this out by accident. Appearetly there's this Adler's Key that spawns right next to the save point in this certain Vol. 2 Main Story Dungeon. And it just spawns again after loading the game so one can just collect - save - load - collect - save - load - ...
Appearently you'll need to collect 100 of those if you want all the Lost Weapons in Vol. 2. You can only carry 99 at a time, though.
Currently, Windflare has 654 views for .hack//G.U. Last Recode across 1 video. Less than an hour worth of .hack//G.U. Last Recode videos were uploaded to his channel, making up less than 0.00% of the total overall content on Windflare's YouTube channel.