If I remember right the "mega 25" was actually a 40hp 2-stroke model (I could be wrong about this). It was sold back in the 80's. I'd be surprised if any of them are still around. I don't think Tohatsu USA even has any info on them any longer.
I am still running my Mega, change the water pump every two years or so, has been the best outboard I have ever owned. I am limited in some areas by CC's, but most refuges and reserves honor the 25HP stamp on the motor. It allowed me to bring 3 or 4 kids fishing and always be able to handle the boat without being underpowered. Most of the shops here in SW Louisiana still stock teh parts for this motor, which are essentially the exact same as the 40 hp Tohatsu, just FYI,
This is a detuned D series 40. Made in 1993. Great motor. If you run across one but it no matter cost or shape. Can still by parts power head etc from factory..The Yamaha 25 3-cylinder 2 stroke is a very strong motor. Last made in 2002. Can put Tohatsu or Nissan 40 carbs, open exhaust tuner and rip on a 15 x 44 flat or semi v around 42-47 MPH...