You might think this trophy is easy to pick up in a normal play through - after all, you just need to buy all the weapons. Right?
For the most part, yes. However, there are 3 weapons you will not get this way.
First and most obvious is the RYNO. In order to get the RYNO, you need to gather all 10 spybots, then visit Ms. Zurkon.
The other 2 weapons, the Bouncer and the Pixelizer, are easy to miss. These can only be bought in "Challenge Mode", which is this game's name for New Game Plus. Finish the main game, start a challenge mode save, and then play until the first Ms. Zurkon.
If you buy the Bouncer and the Pixelizer from her, and you already had all the weapons bought in your main game save, the trophy should pop.