Those little things do take off when they hit the ground. I don't know why this don't mushroom them a little more so they stay on. Next time I take the Baker Wings, I may just tack them on with a little super glue.
If you are talking about the stick-on rubber bumpers, you might try an arts and craft shop or a hardware store. Seems as if I have seen about 4 of them on a sleeve before. Or, you could contact Baker Wings themselves.