Here are some additional information...
If you still have your ticket of the bus you took, there might a contact NO. on it.
Or maybe on your receipt.
If you remember the bus companies name, you can directly make a phone call to ask them if they correct your stuff.
If someone found somebody's stuff, we Japanese deliver it to Lost-and-Found, and it happens a lot, even if that stuff is your wallet.
You can ask at the police station/Police box if you are not sure that you lost it IN the bus, possibly around the station or else.
If you write some papers at the police station, they will let you know when it's found even if you are back in your country.
Hope this can be your help...!