You get the beans out of rare seed packs on ps4, and the stump is always available for purchase in buy mode. No need for any cheats.
I 'm almost certain your correct in that there is no plaque to receive for that collection however, not all collections have a plaque as a completion reward, decorative eggs collection for example. I'v completed the bean collection on several different games and never seen a plaque, I think the "reward" is exactly what the wall note states upon completion of the collection in that you can plant them all in the stump and "water it to see what happens".
