Your local cat thief does not have connections overseas. This market only exists because domestic purchasers aren't regulated.
No, but there would probably be some middleman who has connections overseas, and would collect/ship converters for a fee.
Well, it starts locally. A meth head stealing a converter isn't going very far to sell it. Odds are most are sold to junkyards that sell them to a larger recycler that processes the PGMs.
I think it's a bit of a stretch to assume that entire illegal market could move offshore without a trace.