Here is a quick simple answer for you, goto your gamecore\guns\ and whatever gun you want to know if it has airmod ability. Open the gunspec file and scroll down and see if you see something like this in it:
;AirMod Settings --------------------------------------------------------
noscorch = 1
soundstrength = 20
runy = -2
simplezoomspeed = 7
gunlagspeed = 14
gunlagxmax = 10
gunlagymax = 10
recoily = 100
recoilyreturn = 80
recoilx = 3
recoilxreturn = 95
;simple block animation
;block = 188,203
If it does then you have iron sights or whatever already included. If you do not have it then you will have to edit those files in order to have it. Here are a few people who have asked the same question and some of them have already made it possible without a mod. Here are those links :
http://forum.thegamecreators.com/?m=forum_view&t=150089&b=21
http://forum.thegamecreators.com/?m=forum_view&t=155886&b=3
http://forum.thegamecreators.com/?m=forum_view&t=140659&b=24
But also you could finish the search or ask the master himself EAI for a good tutorial on it. Here is something that he did :
http://www.youtube.com/watch?v=v75f6RnBcTU
I hope this helped a little.