Buying Green Car Ticket for Marine Liner

I have a nationwide JR pass, which will allow me to ride the regular seats on the Marine Liner train from Okayama to Takamatsu. But I want to sit in the green car so I need to get a ticket for that. Has anyone done this recently? Can I purchase just the green car ticket at a machine, or do I need to go a staffed ticket counter (Midori no Magoguchi)?

You can buy the green car supplement at selected ticket machines (the ones which allow for seat reservations, but I am not sure whether the English version interface supports the particular service) and at ticket offices. If you read Japanese, you can also buy it via the e5489 website, in which case you can actually get it for 470 instead 1000 yen (you may also require a Japanese address and credit card in order to be able to use it).

Marine Liner runs between JR okayama st to Takamatsu.you need 1000 yen for green seat
Or 330 yen for reserved seat,0 yen for non reserved seat,base fare is 1660 yen

Or 330 yen for reserved seat

No, the reserved seat fee is fully covered by the Japan Rail Pass!

Thank you for the input!