Sagano Scenic train ticket

Hello to all. I wanted to book a ticket to the Sagano Scenic Railway. I tried to contact some agencies listed on the site but they said that is not a service they offer. you know tell me another way to book or an agency that will surely offer this service. thank you
(I care to book because I saw that some trains are already full)

You need to go to a JR office in Japan.

OK thanks. I'm still hoping to contact the office to try to reserve a seat . we hope well
thank you

As I am also planning to take this train for my upcoming visit, I contacted the train company through their japanese website a couple weeks ago and got the following reply.

We are sorry, but you can't purchase the advance ticket oversea and online.
When you arrive to Japan, you can purchase it at JR West Green Counter or Japan Travel Agency.
If it is sold out, you can purchase the day ticket at our company station.
We sell it in order of arrival.

Car 5 is open-air, so you cannot take this car in rainy weather,
tickets are sold only on the day and cannot be reserved in advance.

JR West Green Counter is available at the airport and major stations like Osaka station or Kyoto station, so the best way is to buy the tickets once you arrive at the airport/kyoto. There are 8 trains (9 during peak period) each way running per day so I don't think it is that hard to get a seat.