Hi Chris,
There's quite a few options out there, varying in price.
The one you have pictured is by JTW Astronomy and is available on eBay.
https://www.ebay.com.au/itm/Skywatch...frcectupt=true
Locally available option Paul described:
https://www.siderealtrading.com.au/p...adapter-plate/
Overseas options:
https://www.astroshop.eu/accessories...mounts/p,57934
http://www.tpiastro.com/Custom_pier_adapters.htm
You might also consider contacting Joshua Bunn to see if he can make one for a good price.