Hi mikster
Its a nice place to visit in Tokyo and Osaka
Which airport are you departing? Haneda or Narita?
How do you get to Osaka? By bullet train or domestic flight?
Or perhaps are you flying out from Osaka, Kansai airport?
The model Seiko Sumo is usually available in the popular watch store in Japan.
The most popular watch store that you could visit are
BIC CAMERA or
YODOBASHI. They sell almost everything and they have a watch department in the shop itself and have many branches in Tokyo and Osaka. These two are usually situated at the train station or within the vicinity.
If you are taking a train between Tokyo and Osaka any major station stop you should find out the store by asking the Information counter. The bullet train station that you take the train is Tokyo station and there is one branch there. You could check their branches from their website if you have to take off from other station.
Last month when I came back from Kansai Osaka airport I can't remember if they have a Sumo there but there is one Seiko Shogun. Most of the watch shop in the airport that I observed have dress watch and not many diving watches.
In Haneda airport I remember too mostly dress watch when I was there in February. I have never seen a Marinemaster in these two airport.
Having a bigger wrist like yours the Sumo suit you well. I find it a bit bigger on my 6.5 in wrist. But I like them.
The setback is the accuracy which is not within the COSC that's all I can think of.
Here are 2 wrist shot. I have replace the bracelet from those of Yobokies.


Good luck in your hunting