They don't make it(yet).
No
search Portal gun DIY indymogul on you tube for instructions on how to MAKE your own portal gun
In the game Portal, yes.In real life... there could be something called a portal gun. But there's no known way of making something that works even approximately like the gun in Portal.
you can play mario bros with portal gun online
No
The only gun there is on portal 2 is the portal gun which creates the portals. You shoot a portal on white surface, and shoot another portal on a white surface, and you can move yourself and objects through these portals.
no
yes
Well, unfortunately it is impossible to make a portal gun without the mod. Sorry.
No
To be able to shoot the blue portal gun, you must aquire it. To do so, goto testchamber 2 and, you will find the portal gun. Simply reach it, by steping through the portal it shoots, and then grab it. Then, you only have to click the left mouse button to shoot it!
Try google