So you're wanting:
-No weapon available at start
-Hold down a key to show weapon and slow down player
-Release key to hide weapon and speed player back up
Right?
In Ply's Mod it would look something like this:
:state=0,keypressed=34 1:giveweap=scifi/tavor,plrspeed=75,state=1
:state=1,keypressed=34 0:removeweap=scifi/tavor,plrspeed=100,state=0
That'll make it so when the player presses and holds down "G" it will give them a weapon and slow down the player. When they let go of G, it takes the weapon away and speeds the player back up to normal speed.
The one and only,