So I got the Y-Wing model today and noticed that there is not real turret on it.

Does anyone have modeling experience? How can I make a mini turret and glue it on to my Y-wing?

 This is something I've been pondering as well. I'm sure it would be easy to cobble something together using wire and plasticard. 

 It's not really noticeable on the BLT-A4 Y-Wing which was the variant used at Yavin.

http://starwars.wikia.com/wiki/BTL-A4_Y-wing_starfighter

your local game store should have some "Green Stuff".  It's a miniatures industry standard sculpting/molding medium.  It's a 2 part epoxy, [blue part] + [yellow part] = [green stuff] to sculpt with.  It is very tacky when malleable, so it will stick nicely to your miniature, and is a bit like sculpting with warm chewing gum.  I'd recommend playing with small bits on test pieces before going at your miniature with it.  Water and a sculpting tool makes nice smooth surfaces, and it really is fun to play with.

There is also "Brown Stuff" that is used for hard-edge modelling, but I find that green stuff is sufficient for most applications.

There's a ton of information online for all miniature sculpting materials and methods.  Have fun! 

Was slightly disappointed by this aspect of their Y-wings, but I'd rather have no turret, than one more piece that would be super easy to break and annoy me even more!