There are C0 Newcastles. I've seen a few reports of people getting them lately. Not enough to give any indication on what your odds are though. There are also CG Clawhammers, which is what I recieved yesterday from Newegg (OEM 3200+ Clawhammer). I don't think I've ever seen a mobile C0 revision, those are all CGs, so that's the best way to get one. The downside is all the motherboard issues, which is why I went with a desktop chip. Anyway, you could end up with either revision on either chip, so don't assume one way or the other unless you know for sure what chip you're getting. I wouldn't put too much stock in the model numbers that vendors list either, unless they specifically guarantee it. Most don't keep that up to date and probably go through stocks of both C0 and CG revisions without changing the model number. Case in point, Newegg listed my chip as an AP but it ended up being an AR anyway.
As for motherboard selection, I went with the MSI K8N Neo, and it seems to be working out pretty well now. There are some temp sensor issues, which are pretty annoying. I thought it was only for Newcastles, but I'm definitely experiencing it with a CG Clawhammer. Other than that I'm happy with it. I think all of the currently available 250 based boards are looking pretty decent, just pick the cheapest one that includes all the features you need.