I put this together based on the information I got from The Home Foundry forum: http://forums.thehomefoundry.org/index.php
I bought the thermocouple from MIFCO: https://mifco.com/shop/thermocouple-for-ht-furnaces/replacement-8-thermocouple-tip-2/
I bought the display unit (thermometer) from Clay King. You have to scroll down the page to find this specific unit: https://www.clay-king.com/pyrometer.htm
The Fusion 360 model for the bracket is here: https://a360.co/3CQUve1
I haven't done any refinement to the 3D model. If you make any adjustments, please post a link in the comments and I'll update this description.