re: Sales Tax question: re: drop shipping to a FedGov end-user for a reseller account

Sales to the federal government are not subject to sales tax anywhere.

Sales to fedgov contractors, it's a little more hairy. Some states exempt, some do not.

Is Company B considered a fedgov contractor?

If company B is reselling, why the heck won't they provide a resale certificate? That would be the easiest way to go because then Company A can just fall back on that to not collect.