I would not expect there to be a US distributor of these; they are far too niche. I think your only options will be that auction site, or one of the major online Japanese hobby shops like Hobby Link Japan or Tokyo Hobby. I think buying from overseas is likely going to be your only option.
Besides the sets, Fujimi also sells photoetch details for the ports, and boxes of just the ships on sale in the 1/3000 line too. But, they are all Japanese subjects, and unlikely to be a target for someone to bother importing.