Dawn,

You can buy any cable with 3.5mm Male Mono Plugs on both ends. You can use a cable with 3.5mm Male Stereo Plugs on both ends, but it may be slightly more expensive. It's also easy to add plugs to both ends of a wire if you've run the wire through wall or conduit.

I did a really quick google search and got the following.

[Link: cablestogo.com]

Note that I have not used this company so can't tell you if they're good, but they've definitely got a selection of 3.5mm stereo cables on their site.