I tried to modify my save game using the Hex Workshop. I really don't understand anything about hexadecimal e modifying it, lol. But, I noticed that the new parts are unlocked after you advance the player level, acquiring a better ranking.
Well, i tried to do this on Mission 01-1, and then i compare with a older savegame o HexWork... After this, i made some crazy modifications (as if I know what I'm doing...), then when I reload the game again, I was in Rank S, and all the parts are available on shop!
Buuuuuuut, on my modifications I've change something that i couldn't, because my Workshop Capacity on game was at "0", and the save gets bugged, cause even if I sell some parts, I still with zero of Capacity, then I couldn't buy the new parts...
(sorry for my english)
well, I don't know if the image will help you to locate where you can do this modification, but if you do this, like your money editor, it will help a lot!
The others yellow lines down the part i've marked, I made modifications before this one, i think that it will don't change the result... i think.
I'm still trying to win the last boss... maybe new parts could help. hahahaha