I'm not too sure DH Gate and/or AliExpress would be the best place to do a search. Being Chinese sites we there is no guarantee that the products being sold are authentic.
Gatsby has official sites in a number of countries around the world. I have sent an inquiry on your behalf about wholesale/bulk purchases. I will be in touch as soon as I hear from them.
I did stumble on this site - Link hidden: Login to view
They seem to offer Gatsby products at whole and accept safe payment methods. However we cannot vouch for them as we have not done any prior transactions with this supplier.
All the best! And welcome to our community :)