Mercury vapor lamps usually go up to 2000 watts, but are there any examples of even higher wattages out there? Metal halides used on fishing boats can go up to 10,000 watts, so i assume a mercury vapor bulb that powerful is possible.

I think GE made a 3000w MV lamp and ballast back in the 1940s or so.

I know both GE and Westy made the 3000 watt T-9 1/2 lamps into the 60's . I'd assume Sylvania did too .

Yeah the linear H9FJ lamp. It was used in long reflector luminaires that resembled the fluorescent luminaires at the time.

I'm not sure if Sylvania made one, it doesn't appear in the 1964 catalogue although by then, the 3000w MV was probably on it's last legs in terms of manufacturer support. 

The 3500W H9 was an interesting medium pressure lamp with hardglass arc tube. 

In Britain there was a fairly common 5000W quartz lamp, mainly used for photo-printing and actinic / UV applications.  For long diazo print lamps ratings up to around 20kW also existed.  See for instance http://www.lamptech.co.uk/Documents/Datasheets/Thorn%20-%20Datasheet%20-%20D%20MS%20-%20MB%20Photoprinting%20-%201985%20UK.pdf

I just got a warning from Firefox that your site isn't secure trying to download that file, James..! Never had that before.

I only realised the other day when someone asked about it that it doesn't use https, is there a reason..?

There have been higher wattage mercury lamps-water cooled used as projection lamps in cinema projectors.Used before xenon projection bulbs.Sony built a digital cinema projector that was lit by a special mercury lamp developed for that projector-now no longer used and Sony has discontinued cinema projectors.Don't beleive you can get the Sony mercury bulbs anymore.