Good luck. They are pretty much non-existent in the USA.
I was looking for one a few months ago and had a hell of a time finding one. I e-mailed Bob Roberts and he said that he didn't know of any left in the USA. I actually stumbled across a vendor during a Google search and found one. I just checked their website today for someone else, and they now list it as "not available." I'm assuming you have the Hantarex MTC3000 monitor in the machine, but you should check. They sold those machines with two different monitors: Hantarex and Tripole.
What I had done in the meantime was to buy a 9" B&W CCTV monitor ($40 shipped). There is an output on the DRT board that will allow you to output to the monitor. It worked great. Now I'm keeping the monitor in case the Pub Time one goes out. Then I will either gut the CCTV monitor from the case to install it into the dart machine, or I will just run the coax cable to it.
Just to give you an idea what to look for in a CCTV 9" monitor, here's the one I bought. It worked perfectly with the Pub Time Premiere.
http://www.ebay.com/itm/19064592865...NX:IT&_trksid=p3984.m1497.l2649#ht_782wt_1398