Same sort of deal as the 32X, I'm going through a ridiculous amount of trouble to get another system that nobody but me cares about. Grabbed one on half.com for $15, missing the requisite cables. Not having any fitting AV cables or AC adapters with the required voltages (or when I did, they didn't fit into the system's plug), I thought I'd try some generic parts at Game Force. While it powered on with their provided AC adapter, their generic RF switch just wasn't cutting it; the picture was so out of whack I could barely make out the huge "SEGA" logo when I turned it on.
Fortunately, doing the research, it appears that Master System parts are much easier to find than 32X parts. That said, they're not exactly cheap either. Ah well, I get paid tomorrow, I'll sink a few bucks and give it another try in a week or so.
UPDATE 12/27/07: Plunked down some cash on sega-parts.com and ebay for an A/V cable, AC adapter, and a controller. I also have a second Light Phaser on the way due to buying one on eBay before I checked out Game Force's SMS stock. Mysteriously I got a $3 discount on the A/V cable, so I didn't end up spending as much as I thought I would. Always a plus. I'll update this post again when the swag arrives.
UPDATE 1/4/08: Stuff arrived today. Plugged it all in and gave it a go. It's all working good with the lone exception of Wonder Boy in Monster Land; apparently it's not compatible with Sega Genesis conrollers. Ah well, I've got a Master System controller on the way from an eBay auction I won, and with that extra Light Phaser I can get some two-player Gangster Town action going on.
UPDATE 1/16/08: Late update, but I received my extra controller and Light Phaser and everything's running smoothly now.