I received a 4734d form and don’t feel comfortable mailing that info nor do I have a fax machine available to me. What can I do to answer their questions?

If you do not want to use USPS you may consider a private mail delivery service such as UPS or FedX.  An other option would be to use the fax services at UPS, FedX or other business mail center.

I’m stationed in Japan and don’t have that ability.

As you are stationed in Japan you may want to call the CA FTB at 916-845-7088 and explain your situation to see if you can provide the information in some other way