Matthew Doucette:I thought if I bought a sound effects CD or DVD filled with explosions, futuristic weapon firing, etc., it would be much easier to fill in the sound effects we need.
As a general rule of thumb, you can frequently type whatever you want in a browser's address bar - as though it were all one word - and then just add .com to it.
You'll find that sample CDs are not cheap, and that the ones you can buy inexpensively don't always give you the license you want - they're often intended for people to use when performing live (the BBC sound effect libraries used to be notorious for this, but I haven't looked at them lately).