I do not know of anything but I am thinking.
What are you amplifying? Sign wave, pulse, square wave?
1) 300V pk into 50 ohms. (600V p-p) I have used AM broadcast transmitters that can do that. (sign wave only) 100%.
When you say 5% and 10%; Is the output a pulse that is off 90% and on 10% or will the amplifier be used for 1 second and off f10 seconds?
While lightly off-topic, I couldn't help but notice that your proposed frequency ranges fall into **broken link removed** (pages 2-5).
Where are you located? Are your load(s) dummies or antennae?
If using antennae, pumping out a few kilowatts (even if only a few milliseconds,) can attract a lot of unwanted attention (since it's illegal to do so without a license).