I'm not aware of any modern maker of 24 tooth freewheels, but they're actually pretty common on Ebay - if you trust 50+ year old bike parts. So far I've had no problems...
<edit> Because it's been years since I last looked for large SS freewheels, I took another good look around. Turns out a place called Circle A Cycles in Rhode Island appears to have 24, 26, 28, and 30 cog models in stock for $85 a throw.
Last edited by Six jours; 01-01-12 at 07:21 PM.