I was kind of wondering about that too. For a few weeks I was highly undecided about what I was gonna do about mixing some P90 action into at least one of my guitars and either an actual Chris Robertson or at least the concept of sticking a P90 in the neck slot of some other guitar was near the top of my consciousness. And there were almost no Chris Robertsons to be found. I think Willicut in Kentucky had 2-3 in stock that showed up on Reverb and I didn't see any others anywhere. I'm sure there might be some big PRS dealers that have them and don't advertise them except on their own sites, but none of the big mainstream dealers had any listed. And I'd assume at the SE price-point, that's where a lot of those guitars would sell. Sweetwater and Guitar Center (and affiliates like MF) all seem to stock plenty of Zach Myers and SE 245s and whatnot, but no Chris Robertsons. Maybe P90s just aren't very popular. I think Ibanez sells quite a few of their excellent semi-hollow guitars, but they sold a hollow body P90 version (essentially a knockoff of an Epi Casino) for a few years, but killed it off pretty quickly. And it's a pretty tough model to find used even though it was for sale up until 2-3 years ago. PRS isn't selling any SE soapbar models these days other than the Robertson.
I've just recently really gotten into P90s - LOVE those things - but they must not be very popular among the buying public...
-Ray