Ahh I can see your problem 
Japan is a very popular destination, but there are not a huge number of members there. A few suggestions - firstly please do share your link to your listing as you never know who may see this post. There are various articles on the Forum and the main website about how to best write an exchange proposal, such as this one: How to Write Your Exchange Proposals - Advice from Lou Make sure you are personalising every request. Are you looking for a Guest Point exchange? Can you open it up to a reciprocal, either simultaneous or non-simultaneous? Have you tried doing a reverse search? Also it might be a bit late in the day, but also try adding this trip to your Preferred Destinations list with the dates.