Japan is very sparse when it comes to private jets (or privat aviation of ANY form).
Throughout Asia, the Learjet is not very well represented mainly due to its cabin size and range - neither of which are suited to the distances between A and B.
There are less than a handful in Singapore (not Singapore Airlines which are in Australia anyway), a couple in the Philippines, a few (LR-60's) in Malaysia, one or two LR-31's in Indonesia.
C2j