Huntington's sells .30-'06 Basic Cases (http://www.huntingtons.com/cases_howell.html) made by Howell, which I believe are simply unformed straight walled .30-'06 brass. With the proper forming die, it would be a simple operation to create cases which would be a perfect fit for your chamber, without the risk of a case splitting. Despite WR's abandonment of the cartridge, it makes perfect sense as far as cartridge design is concerned, since the sharp shoulder and parallel sided case both headspaces better and is easier to extract.

Incidentally, it is possible to fire form .30-'05 Basic Cases using an otherwise useless barrel and action. The process is spelled out in detail in Nonte's book "Cartridge Case Conversions". If you are interested, I can scan the passage and forward it to you.