I know you used to be able to get tons of a particular item by cheating using a specific procedure, but that stopped working sometime around last Thanksgiving. For the record, here's the procedure.
You need at least two of the item. First scan for the value of the number you have. Now give one of them to one of your manamon, scan again, then if you have more than one left, give another to a manamon, scan, etc. If you get down to one of that item in your inventory, take one away from a manamon, scan, etc. Don't ever let the number of an item go down to zero or you have to start over. I've given myself tons of levelups and other things this way. In fact, I was so frustrated by a particular point in the game, having managed to find only one levelup herb up to that point, that I purchased the game a second time so I could trade with myself, transferred my primary save to my second computer, gave my only levelup herb on that computer to a manamon and traded it to myself, then removed the levelup herb from that manamon back on the primary computer so now I had two levelup herbs so I could cheat.