To avoid frying the actual Diode Junction, The do NOT drive them with DC. You supply (usualy 3 to 6 ) volts to a very smal pulse circuit which actually drived the diode. It's not like a regular, or high output, LED. Run em on DC without the pulse circuit, or cryogenics, and you will hear a little 'POP', your diode will turn a grey/brown color, and you'll be shopping for another Laser Diode....
Don't ask how I know, or how stupid I am for having to go through it more than once before I put an oscilloscope on my pulse circuit (turned DC converter).......

You can, if you can find them, buy small laser dot assembllies, housed in a brass cylinder, with the pulse circuit inclosed (the brass cylinder makes a nice heat sink). Supplied power is not an issue, as the pulse driver limits what goes to the diode. I've run mine off a 12V carbattery and off a pair of AA batts. Got mine from a parts house in Dallas TX (BG Micro??), but Google is your friend.

Aligning the laser to the gun's point of impact will be a fun project. Remember that laser's light goes in a straighe line from point A to point B. The BB from the Airsoft doesn't.....

Be interresting to see how you come out. Good luck with it.
Splat