Harris Cyclery has a fair amount of info on this subject and they carry some pretty small rings.
http://sheldonbrown.com/
Don Martinich Davis, CA
> Hi everybody! I'm thinking about a drivetrain change and need some
> info to see if I'm on a dead end road, or not. For the TA Pro5
> Cyclotourist patterned cranks:
>
> * Is a wide range of chainrings still being produced, or is
> everybody working off of old stock?
>
> * Do you know who stocks a wide variety? (I don't see many at VO,
> PWCycles)
>
> * I've heard of inner rings that bolt directly to the crank flange,
> allowing rings as small as 19t to be used - can somebody verify
> that, and point me to a supplier of tiny, compatible rings? Does it
> work well?
>
> The context of all of this is that I'm thinking about making a
> 44-20ish touring double. Have any of you ever set up anything like
> that? If so, did it shift reliably? I'd expect the shifting to be
> anything but crisp and quick, but it needs to be reliable, non-
> jamming. Do any of you have any insight or experience with similar
> arrangements?
>
> Thanks,
> John Clay
> Tallahassee, Florida
> USA