The first place your buddy needs to call is Stoeger Canada or visit your local LGS that sells Beretta. Stoeger sells non-catalogued Beretta parts/accessories to the public. Anything else in the catalogue needs to be ordered through a dealer. If he purchased the gun new, it will be under warranty but he may need to send it in. They've replaced forearm caps twice for me out of warranty. If the story is convincing, they would likely do the same for a plastic spring sleeve.
From my experience they don't often return calls to the public right away until you get in contact with a human. Once you do, take down their name, phone number and email so you can follow up. If the part is in stock, they'll have it out to you within a week or two. Might be better off contacting their customer service/warranty department first.
I've also been there in person to drop off something for warranty. The parts are located in the same location of their secured facility and can be seen from behind the counter.
