I found these bolts and springs on the floor of the garage on the passenger side of the car near the middle of the vehicle. They appeared on two separate occasions, one spring/bolt combo at a time. In both cases, shortly after having the vehicle serviced. No dirt or rust, but fresh grease. I keep my garage clean and cannot determine where these might have come from. An inconclusive google search for similar springs turned up evidence that they might be associated with some Forrester models, but, as I said, the search was inconclusive. I appreciate your help and input.
(If someone's using my garage for secret projects while I'm not at home, I think I've got bigger problems. )