According to this thread:
https://www.airgunbbs.com/showthread.php?893763-HW45-rear-sight-question&p=8130373

The rear sight is the same as a HW45. Certainly looks the same in pictures. Available here: https://www.airgunspares.com/hw45rearsightweihrauchhw45rearsightassy.html

I have a HW45 if you want me to take any measurements