[Anamensis]

Why would a bunch of first century Jewish sectarians think their rabbi rose from the dead, and why wouldn't their enemies simply produce the body?

Why bother? I doubt anyone felt that a handful of lunatics was important enough to dissuade. The main troublemaker was dead (in their opinion), so let his left-behinds wander around the desert talking about him. Who would care? They were't a significant force.

[A.J.Armitage]

You only addressed the second part, not the issue of where they'd get the idea Jesus rose from the dead in the first place.

As regards the second part, it doesn't fit with how we know religious fanatics with authority act. A Jewish Grand Inquisitor would try to root out any trace of heresy just as much as a Christian one would. And we know a particular Jewish Grand Inquisitor did go to great lengths to stop the troublemakers before becoming a notable troublemaker himself. And besides him, there are early Jewish anti-Christian polemics that have come down to us, so obviously Christians were important enough to at least write against. In fact, some of the details in the Gospels were included to refute these polemics, which means that at least some of the Jews paid attention to Christianity very early. Which leads back to the question: why not just produce the body and put a stop to it?