Right now I'm looking at the Vonnic A2812. It is a field monitor, color bar generator, portable power supply, and it seems to work most PTZ controls from what I can see.
In the features, it says "Video Level Test: Video Signal Measured in IRE or mV" -- Does this do what you were asking about?
Anyhow, it's about $225, but NewEgg has a 25% coupon code running for Vonnic stuff that brings it down to like $170. The code is "VONNIC25".
I'm looking to pick one up, so does anyone have an opinion on them?
http://www.newegg.com/Product/Product.aspx?Item=N82E16881618183