I've been looking for one too. I usually just setup the DVR first and use my phone to tune the cameras. This is the first actual test monitor I've seen. It will help with troubleshooting, and focusing varifocal cams.
http://www.ltsecurityinc.com/ltax41t.html
This is a Hikvision unit rebranded by LTS. The default Admin login is admin:12345. If this doesn't work, the previous owners changed it. You'll need to contact LTS to have it reset. There will be a way to reset back to default, but I don't know it.