Slingshots are illegal in most states, some states allow "pest controllers" that arent slingshots, honestly It can be trivial crap like selling handle and band separate, this was case in vic for couple of years prior to the banning.Technically they arent banned just regulated anyway, legal imported ones get serialized just like a firearm and theres licensing and registration, it would be laughable if it wasn't sad!
A little bird told me as long as its not braced, they can be purchased online and make it through customs.
As for the inert plastic BB's, that's just beyond full retard.Yup id be looking at raw plastic material or theres also these "microspheres" stuff they mix with resin when doing fiberglass(mates a boat builder) that would work well.