The best vacuum we can produce on Earth can certainly arc. It used to be the bane of my life since defending computer control systems from such flashovers was somewhat tricky. Mass spectrometers tended to do it from time to time if the beam current got a bit out of control or there was a trace of just about anything on the stand off insulators.
Even the deepest space voids there are still a few protons and electrons about. And everywhere else there is slightly more stuff.
Most researchers think that the intense magnetic region over the poles would be good candidates for the right sort of conditions.
Ultra strong B fields are relatively common in compact objects since the stars magnetic field remains trapped in the conducting plasma as it shrinks in size. It isn't known what the upper limit for this is exactly. It is almost certainly enough for pair creation though.
This is just about accessible if you are interested (a bit dated). I couldn't spot a popular science level version that was half way decent.