Don’t know exact situation of your business, but yes, as visiting Japan as a tourist likeliness of able to open a bank account in Japan is almost zero.

I guess my question will be why do you see the need to have a bank account Japan? What will likely happen is that money transfer need to take placce as below:

Your Customer’s bank account (don’t know where your customer is located) –> Your bank account in Singapore (Is this where you are home based?) –> Supplier’s bank account in Japan.

By some reasons you want to avoid above situation?

P.S.
mrploddy posted before me. I did not mention what mrploddy described, because that requires OP to handle transaction in cash from the customer to the suppliers. Since this is a business transaction so OP may be talking more than few of ten thousand yen of cash.

I guess Japans is more of cash society compare with the U.S. or Western European countries and banks branch offices in Japan likely do handle more cash transactions…