considering doing a full rewrite of a mission-critical VFP application ... (a VERY extensive/expensive project) is the fear (justified??) that "good" VFP developers cannot be found

There is a way to shop for a good VFP developer: You ask for work samples (SETUP.exe, user guides, copy of project proposals that translated to a complete BIG project, and references. Big projects do not imply a a big development team. A successful team would be the user audience and experts within that audience that have the technical expertise to describe and support functional requirements.

that "good" VFP developers cannot be found and/or would be very expensive compared to Java, C++, .NET, etc. developers.

Not neccessarily true. A big company (here) has spent over 1.2 Million on a team of 20 VB.NET developers. The project was supposed to be delivered in 10 months. After two years of development (and, of course, the 1.2 million), and a year of parallel entry (few of the computataions have been correct, and the hour glass seems to have a permanent residence on the desktop) and bugs that go ad infinitum - they are close firing the VB.NET guys and looking at proposals from a VFP shop that has a good delivery record.

Paying one or two VFP developers 400K (that have a good references) to deliver (and integrate) on schedule can be a lot cheaper than thowing in a bunch of dough for a "team" made up of individuals that say "yes sir" in lock-step, yet, do not have a delivery record can (and will) be more expensive. The bet (or con:-) big team project managers wage:The client will reach the point of no return and and say, "We've already invested almost a million more that the estimated cost" - we can't turn back.