You can get this by simply saving at a U-Invent machine, inventing whatever you have enough components for, exit out of the U-Invent and reload your save. Quick, simple, and you save a lot of time by not having to worry about scrounging for enough components all throughout the game to get to 100 items! I just wanted to see if this would actually work so I tested it out at Farmer's Market and sure enough it worked for me. When I invented the items I could, I exited out of the U-Invent and when you exit out, you can see in the upper right of the screen how much you have created. I waited for that to disappear and reloaded my save because for some reason, the first time I did it, I tried to reload the save while those items were still showing at my screen and it sent me back to a different save.