That's frustrating...
Checked several Japanese online stores and all of them have the same issue: no international shipping with Japan Post since they suspended the service for USA. Only expensive services like Fedex and others.
Why!?
Japan Post Suspends Mail Services to the US Amid Tariff Uncertainty
Japan Post has temporarily halted its regular mail services to the United States in response to ongoing tariff issues between the two countries. The suspension, which was officially announced on Japan Post's website, is due to the lack of clarity regarding how these tariffs will impact international... [More info]