I think it is wonderful that you know what you want.  Now let me help your quest.  First, let me tell you that you are very lucky that you live in this day in age.  Through the use of the internet, people who would have never met before can now become acquainted even though they live thousands of miles apart.  They can correspond with ease by using e-mail and VOIP phones and they can ask all sorts of questions of each other before spending a penny on an expensive night out on the town.  I met my American husband on the internet.  We corresponded for one month and fell very much in love.  By the time we met face to face, we were very excited with anticipation and we shared some very passionate moments.  You too can experience this just by doing some basic searches on the internet.  

In these search services, you can input the ethnic origin of the girl as well as specify where she currently lives.  I am sure with such a search, you could easily find profiles of single Japanese girls who already live in Singapore.  Also remember that you can leave your profile too so that the ladies you seek can find you instead of you always looking for them.   

If you are still skeptical about meeting people on the internet, keep in mind that it is much better than cruising bars, night clubs, and other hot spots unless that's the type of girl you are looking for.  Using the net to find a new friend is a way to find precisely the kind of person you are looking for.  You can ask any type of questions you wish to qualify a person, you are totally anonymous and safe in your home, and if you don't feel anything special with your new friend, you don't have to feel sorry about him or her if you choose not to correspond anymore (but be honest, and reply with your feelings as it is not nice to just leave a person wondering.)  If you do hit it off, you can take it one step further and start sending pictures.  It's up to the two of you how far that could go.  

Later, you can both get webcams and use Skype or some other program to have real-time video chat sessions.  If you still like each other and decide to meet in person, you can use the net to figure out all of your travel plans.  If you then decide to get married, the net can still help you out with all sorts of immigration information that you will need.

If you want to find someone the old fashioned way, I would suggest you seek out Japanese clubs or groups in Singapore.  Generally speaking, "birds of a feather flock together".  You might check if any of the local colleges have Japanese student associations that meet regularly.  Universities tend to have large groups of foreign students who are usually interested in meeting local people who can help them with language and show them around a bit.  You might try volunteering some of your time as a tutor or a driver. You might already know that Singapore is a very popular tourist and shopping destination for Japanese girls and by becoming a volunteer tourist guide you will get many chances to meet them.  It would help if you studied a bit of the Japanese language and history.  Your new friends can help you with that too.  

I think it is really great that you show no preference towards age in a woman, but keep in mind that finding a partner whose age closely matches your own will probably result in a better relationship.  Often times, a guy will seek a much younger woman who may turn out to be a bit more restless than he expected.  An older woman is probably a better choice if you can't find someone your own age.  Keep in mind that on the average, women live about seven years longer than men, and women generally have their peak later in life than men also.