Oh no you cant .........
The `Upgrade ` your refering to is a Rowan Engineering Multi shot Mag . It can be found here -
http://www.rowanengineering.com/products1.htm
The guys make vast amounts of custom parts , and the quality is second to none . I have one for my MPR , and it really is great addition to my `kit ` .
You can contact the guys direct throught their website , or you may find them on AAOC ( Air Arms Owners Club ) Astro and Deker .
In my opinion , a great bit of kit worth every penny .
Buster.
PS , as Davy rightly says for Pesting , yes , but for Tar