The Highest possible manufactured weapon is around 330, that is assuming you were able to get one profitable enough to IPO it and distribute 76% of its shares out to other countries and CEOs so that no one entity has more than 24% control. Otherwise it is somewhere around 312. Most of the Weapons are made by C3's not the GM, because most of them cannot turn a consistent profit. I make a few that now have to be purchased at a Space Dock, even though they cost more to make then they are worth.
Now any equipment that can be deployed to a Mobile Unit can be upgraded to a 600, this is costly and time consuming, so the incentive to disassemble and sell the parts is not cost effective.
I have a lot of leftovers from before the GM dropped the maximum grade to request from the Market from 350 to 330, with the Cash and GC shortages I need the money more than the Stockpiles.