Because it's an Italian gun, parts may be available in Italy that aren't available in the United States.
According to Wikipedia the company has transformed but is still in operation under a new name:
Firearms production at Jager ended by the early 1990s, according to Mr. Piscetta for "lack of skilled personnel". The activity continues though as a gun store and gunsmithing shop located in the town of Basaluzzo, Alessandria province. The name of the enterprise has since changed its name to
Armeria Nuova Jager.
http://en.wikipedia.org/wiki/Armi_Jager
There's a complete listing for
Armeria Nuova Jager including their email address, address and phone number on the following page, 2nd entry:
http://www.bordingl.com/armi.htm
There's also a website named freetranslation.com that can help to translate and compose a message in both English and Italian if that's necessary to communicate with them. Folks need to look to Europe to find parts for a lot of older European guns if none can be located here.
We even have a member here named Rusty.it who is located in Italy and is bilingual. Maybe he can help you out by sending them an email inquiry in Italian. Or maybe he can locate or recommend a parts supplier in Italy.
Here's Rusty's contact page to give him a try.
http://thefiringline.com/forums/member.php?u=50009
Did something happen to your grip frame and back strap that leads to needing replacment or do you just want to upgrade?