I don't have the exact answer to your question, but I did take a look at the files here at RC for Mitusbishi projectors. My guess is that the closest one is for the X300U and I did not see a discrete Power command, just a toggle.
It uses a somewhat different IR protocol from the traditional Mitsubishi commands, but it does not look like another manufacturer. It does seem to have an 8-bit device and 8-bit command structure, so I can generate all 256 possibilities for you in Pronto hex and you can try them to see if you can find them.
The best way to proceed would be for you to learn the commands from the OEM remote into Pronto and email them to me and I can verify that it is this "new" protocol variant and generate the commands for you to test.
The simpler way is to ask Mitsubishi for the commands. I have no experience with Mitsubishi's policy, but other manufacturers have sent back a list of the device and commands (usually in hex but not pronto Hex) and from that I can probably generate the specific commands if they exist.
Also, I have not looked at Mitsubishi's website but some manufactureers are now posting information about their IR commands.
