To get playing with this new weapon in Synergy is pretty straight forward.
* Make sure you have your console enabled in Options (OPTIONS -> Keyboard Tab -> Advanced Button -> Enable Developer Console Checkbox).
Create a server/game. Open the console and type in;
sv_cheats 1 impulse 101
Doing that will give you all the weapons and items you could possibly handle.
You will find the Deagle in slot 2, position 3.