Dual mono tube integrateds

In not sure on this but it may be difficult to find a tube integrated that is truly dual mono? If you are talking about two power transformers, two power supplies and then the output transformers your talking about a heavy piece of gear. If they have chokes in the supplies even more so. You may want to think about mono blocks and a dual power supply preamp? Someone may be able to help you, but nothing comes to mind for me as far as an integrated goes?

Check out the Aronov LS-960I around $1000 used, a bargain.
Dual mono entails using the dual volume controls which are better for performance while representing a slight nuisance for those who don't trust their own ability to hear when the sound image is centered.
I am presuming this is not an issue for yourself, a confirmed dual mono aficionado.
As noted by Detredwings, there is a bit less of the purist dual mono theoretical ideal in a reasonably priced and sized tube integrated.

I just got me first tube integrated a few weeks ago and can't recommend anything in your price range (lack of experience) but will say look for one that has a good output tube protection circuit. I've had mine 10 weeks and have 2 different type tubes blow out on me with less than 50 hrs.