Regardless of how old the bike is they still sell them cant see how why they would have changed that particular part.
So its a bike that is in their current range...this is my question, so it really is relevant.
Unfortunately manufacturers do change tiny items like this. My bike is only a few years old but is a nine speed, very few nine speed blocks available these days.
Just because they sell a bike by the same name, if your mates is an old version it may be a Genuinley obsolete part.
But, as others have suggested, it may also be a common part that can be swapped for something similar. I'm still not totally sure what you are buying, is it a cassette or a free hub. I'm pretty sure that any cassette of the same speed (9, 10, 11 speed) will fit the bike, it may have differnet sized sprockets, which will effect the way each gear feels...but it'll work just fine.
Count the number of sprockets (gears) if it's nine then ask the shop for a nine speed cassette (or block) they will have a few with different sprocket sizes to show you..
What I find odd is that the shop didn't suggest this, which makes me think that the issue is something else.
Good luck.