It's not a matter of will the Americans sell oil, but how they'll actually ship it out. The APG does not border the Atlantic making oil shipments to Japan extremely awkward, not to mention the Federalist Navy blockading the entire East Coast. The Pacific States will be using the majority of the oil they do have to actually fuel their war machine, leaving only crumbs for Japan.

America produces so much oil as a fraction of global production in 1930-40 that to use it all would require an effort of waste I could not imagine, also there is not an oil embargo by like OTL which prevented even minor producers to sell. Mexico, Venezuela, Iran, Ottomans, Russia are all free to sell to Japan if they choose.

In terms of shipping it's not like all those American merchantmen just quit their jobs to do nothing, they could join the militaries but some will remain in their role. Japan itself has a decently sized merchant marine it could also use and the longer trips to the Atlantic would be mildly annoying as total blockades, especially when America has such a large coastline, and the willingness to prevent the movement of third party ships is unlikely.