Hi there,
As you noticed, you cannot find the line to Asahigaoka on the highway-buses.jp website. However, we have buses running between Shinjuku and Asahigaoka.
What you can do is to make a reservation for a round trip from Shinjuku to FujiQ Highland on the website and then, when you purchase the ticket in Shinjuku station, please tell the clerk that you want to go to Asahigaoka and pay the difference.
Please note that not all the buses stop at Asahigaoka, so please choose the bus leaving Shinjuku at the the following times.
[from Shinjuku]
07:15
07:45
08:15
09:15
10:15
10:45
11:15
12:15
13:15
14:15
15:15
16:15
17:15
18:15
19:15
20:15
[from Fuji Q Highland]
07:08
08:18
09:18
10:18
11:18
12:18
13:18
13:48
14:18
15:18
15:33
16:18
16:48
17:03
17:33
18:18
18:33
19:18
20:23
When you get the ticket, please confirm the time the bus is leaving from Asahigaoka because you are ridding from Asahigaoka, instead of FujiQ Highland.
I hope this help.
Thank you.