The scope is a thinkjedi bronze cast. BD offered his service to hollow them and install real lenses. AFAIK the anodized pistons were also from David.
The brass bolts are either from David or CE.
Denix, Wooden mauser grips and the scope mount are generic parts, which are easy to come by. Vince aka CE will do a run of accurate ESB mount next week...contact him.
As an alternative to the bronze scope, try to get your hands on one of the solid MR scopes. I know of many people who replaced the fake scope on their Luke/ Han ESB blasters with real ones.
Muzzle is still offered by Blasttech, not accurate, but good for the money.
Markus