They're very easy to make. You need to go to said Air Guitar shop, because these usually have all the accessories and parts you need, including, if you go on a Saturday, the airhead who works there at weekends 'cause his uncle owns the place.
You'd need to get specialist air screwdrivers and things, of course, but the shop should be able to sell you these.
Of course, the advantages of amps of this kind, like the guitars, are that they're cheap to build and very light to carry around.
As any good air guitarist should know, air guitars don't need amplifiers as they are in fact acoustic and make excellent sounds without the need of an amp
You walk to the back of your air stage (near your IKEA cupboard) with a swagger of "I can crasd my air Roller into thin air if I want to" and twiddle those knobs to 11.