Ignoring devices belonging to Nokia employees:

There were only 250 N9 dev kits (a.k.a. N950s) allocated to be given out as part of the community developer device program. However, an unknown number more are being distributed by Nokia Launchpad to developers with applications in the Ovi Store. Other N950s were given away at in-person MeeGo meetups.

Beyond that, Nokia have mentioned that commercial partners are readying applications for the N9 launch, and in the past, Nokia have enlisted the aid of outside companies for bits as bundled instant messaging protocol plugins. Some developers at those companies may have prototype N9s, but there's likely some N950s in the mix as well.

Some cellular service providers are preparing for the N9 launch as well, and it could be they are using some N950s for their custom development.

In any case, there are far more than 250 N950s outside the walls of Nokia.