You can get ladder chain and sprockets from Stock Drive Products.  They
sell these in several pitches, all metric, but equivalent to inches.
For instance, a 6.3 mm pitch chain is .248" pitch, which is close enough
to the standard 1/4" chain.  All you have to do is get the ratios right.

You can browse around their catalog on-line at http://www.sdp-si.com/
or give them a call at (516) 328-3300 and ask them for the catalog that
contains belt and chain drives.

Regards,

Dennis Mead