digiscoping with RSPB telescope

The RSPB HD 82 Telescope now comes with a Digiscoping SLR adaptor to fit its eyepiece. You cannot buy the adaptor on its own, from RSPB. I already have this scope, purchased some years ago, before the adaptor was included.

Has anyone any idea of where to obtain this adaptor; new or secondhand. Tried eBay but not sure if those offered will fit; eyepiece seems to have a larger diameter than normal i.e. 56mm.

Tried phone adaptor; not keen.

Any ideas please?