Hey Glenn,
Here is the thread that covers what we did last summer with Murudai's Sonar-barrels:
http://www.laserpointerforums.com/forums/YaBB.pl?num=1216368375/0
Here is the switch I used, they seam to work really well:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=SW264CT-ND
If you just need one, let me know, I have some extra I will just send you one. The button will be pretty simple to make, just a thin piece of aluminum with double-stick tape (VHB) stuck to one side.
These barrels are anodized all over, even the threads, this means if you are using the case as you negative-ground, it will not work unitl you sand the areas inside the tail-cap, where the spring contacts the cap, and at the end of the barrel surface where it toches the end of the cap, kind of a pain. At first I thought I did something wrong.
The tricky part is mounting eveything inside the barrel, I made these modules, there is a small pocket that holds the switch, and allows one of the leads to run to the back of the module and connect to a copper-contact for the battery-connection, these are not shown in the picture.
I am sure there are many other good ways too.
