In the meantime, is there a such thing as a small portable external flash or light source?

You can get a "slave" flash unit. Modern flash systems have the camera talking to all the flashes via radio. Back in the not-too-old-days, however, remote flashes could be triggered simply by the bright light from the main flash. Wedding photographers tend to use this sort of gear. See, for example, this photo from one of my cousin's weddings. My flash triggered the remote.

I did some quick digging around on B&H Photo Video (just search for "slave flash"). There's something called a Digi-slave Pro that can be programmed to do exactly the right thing for you. It's USD 240. They've got a cheaper model for USD 150, and the bottom of the line for USD 100. You can also get the USD 50 Phoenix Digital Slave Flash, which seems to include a nice mounting bracket. Of course, I have no idea how well these things do at figuring out your existing camera, but I imagine the "digital" ones do a better job than traditional slaves at dealing with your camera's "pre-flash" (if it does such a thing).

Personally, I've got a Canon G3 (having given my older Canon G1 to my sister as a birthday gift), and I have an external Speedlite 420EX flash. Bigger flashes are the answer to your problem.

If, for some reason, you're hearing the siren song of a new camera, I'd encourage you to hang out until the end of February, when the big photo industry tradeshow happens in Vegas. The pre-announcements are already starting...