Keep us posted when you latch onto something. Did someone mention Federal in another post? ie. they were not as keen on walk-in small qty anymore?
http://federalmetals.calls.net/solid-bar--square-round.html
I'd hate to recommend MetSup for anything, but might turn out to be the lesser evil if you can't source from scrap or somebodies cuttings. It would be a heavy lump to ship if you found online.
I sure wish there was a Canadian equivalent to these guys. That chunk in nice cast iron would set you back a whopping 25$ sold by the inch.
http://www.speedymetals.com/pc-4267-8387-2-14-x-3-14-gray-cast-iron-class-40.aspx
I was thinking about making a mini XY table for kind of a cutter/grinder jig (long story). My limited experience with CI turning my cylinder liner was that it was a bit messy but easy to machine & probably more dimensionally stable. Some chunks of that would probably be good for machine applications like yours.
I want to see that shaper one day. Bring it to the next coffee meeting, ha-ha