If you happen to still be working on this, I made a Pokegear in a somewhat hasty fashion out of foam. (Foam is awesome!)
Basically cut 2 pieces of 1/4" craft foam (closed cell) to form the main body (including the semi-circle) as a top and bottom layer. Then the roundy part on the end I actually used cheap open cell foam (dollar store yoga mat in my case as it's more flimsy) roll until you get the desired thickness, and leave a bit still sticking out as the part that you can glue to the main unit.
Then glued circles on the sides to cap it. One more tiny piece of thin craft foam was rolled into a cone and glued onto the side of the cap to finish off the parts. After that I just painted it up with blue white and yellow - as well as black for the parts that were too difficult to actually cut out - glued a piece of velcro to the bottom and the counterpart to my sleeve cuff and done XD
It is not going to open but it's a decent prop if you have steadier hands than me for cutting and painting. =P