Here's what I've got so far:
1. IEV corp. Salt Lake City, UT 801/466-9093
VGA Broadcaster board does VGA--> composite. $695.
They also make some similar boards for NTSC/RS-170,
S-video & RGB/synch RS-170.
2. Avacado computer. Silver Spring, MD 301/593-5586
VGA-TV card can do composite output for the various video
modes. 64 shade gray scale or 256 color. 256K mem std,
expandable to 512K for $61. Base cost of card was
quoted to me on the phone as $499 but is listed as $699;
they offer a 5% education discount.
3. Video Associates Labs Austin, TX 512/346-5781
Microkey/A card: A rather sophisticated card which can
handle up to superVGA (1024 x 768). Of course composite
video can't handle anything more than normal VGA, at
least as far as I know. The card also has audio capabilities
whereby it can record and play digitized signals to and from
the hard drive. The card is priced at $1495. Talk to Carrie
Cavanaugh and she'll brighten your day.
Thanks to those who replied.
Mike