ScottA made a Poser version of the Roadrunner. His works are redistributable. I don't have a copy to share, unfortunately, but perhaps someone else does.

DAZ's Hatchling Phoenix would make a nice Roadrunner character, with a little work.

Hasdrubal has a number of WB characters, but not Roadrunner or Wile E.

I could probably do something with Furrette for Wile E., but it would require custom morphs and some new geometry to create that lank physique and nose.