Going after demand will be more useful than going after supply.
After all, there's nothing to stop the criminal element from starting up production domestically. (Look at what happened with pot growing - once border enforcement was stepped up, the gangs took to cultivating in our national parks out west...!) So while I understand the need to increase inspections coming in from abroad, it's ultimately a losing game of whack a mole.
We have to instead deal effectively with demand for said stamps - whether that's choking off retail opportunities (going after the online platforms like
ebay, Facebook, etc.) where the commerce actually happens, or penalizing usage (destroying mail with counterfeits, as was threatened before), or getting rid of them altogether.
That's not to say that going after the crooks should stop - I'm glad to read of that recent arrest. But thinking we'd actually be able to intercept an appreciable number of these bogus stamps pouring in is wishful thinking, and thinking that the criminals wouldn't just ramp up domestic production (higher cost, but potentially still lucrative) is wishful, too.