I would say here on Actias.de is the best marketplace for exchanging and purchasing livestock. I tried out some UK website seelling butterfly livestock but I had several inconveniences and delays, so in the end it's better to help us one another in this portal :-)))
I have used worldwide butterflies with no issues the delivery has been next day on each of my purchases. The guy who runs it is very knowledgeable, he has written several books and been around a longtime.
I will keep an eye on the marketplace incase something I am after becomes available.
I'm new in this forum, but just to mention that i've made an order to Matt Simmonds (email@example.com) and i'm very happy with it! Fast and good quality, each week ther is a newsletter with availabilities. He is in this forum as "MattSimmonds".