There's a .38-56 WCF and a .38-56 Improved. Line drawings with dimensions are here. http://stevespages.com/page8d.htm
There's nothing about either on the SAAMI site. Buckets of info via a net search.
The WCF was originally used in the Win M1886. A rifle in decent condition runs $3500ish USD.
Buffalo Arms loads it. Not for cheap though. $60.80 per 20. Uses a .379" bullet.