Hello,
of course it is possible to buy from all over the world. You need the same certificate as you need for your orchids.
You need the sanitary certificate for buying tubers from a non european country.
You also can buy it without any certificate, but it´s on your own risk. Your customs can confiscate the tuber without the sanitary certificate.
But when you buy from US, or an asiatic country, let the tuber ship with an express parcel.
I got some tuber from U.S, which has been rotted, during the shipment
regards
Stephan