The problem are not missing compagnies for safely shipping living Paros across the channel or even across the ocean. There are enough of them, and they need not to be specialized on medical things. And the problem are not the bags, breathing bags or normal ones. For Betta you better take the former, for Paros you don’t need to.
The problem is the costs or better: the aquarists who are not willing to pay higher costs for such services. There are enough fish, enough offspring, enough alternatives. But shipping them safely costs definitely more than a normal letter or parcel. And this is too much for many people. That is the problem.