The rear sights from the XS25 also fit the Ruger Air Hawk. We have them at http://www.archerairguns.com/Rear-Sight-Kit-for-Xisico-XS25-Air-Rifles-p/xs25rearsightkit.htm
There will be photos on our increasing range of Xisico parts pages as soon as I can take them!
Archer Airguns Inc.
Online stores http://www.archerairguns.com