Overnight Train Sapporo to Tokyo area

On Tuesday 5 May I would like to return from Hokkaido (Kushiro) to Tokyo. A while ago I was exploring in Hyperdia (without this exact date) and printed just what I wanted - leaving Kushiro at 13:34 to Minami-Chitose then getting the Hokutosei via Fukushima to Tokyo arriving Wednesday at 8.16 am However I can no longer get this to come up again in Hyperdia. If I can't come back overnight I may have to change the itinerary and fly.
Any help greatly appreciated. We are travelling as a couple and would look for a sleeping berth

Oops, answered yr 2nd later Q.

5 May cannot book Hokutosei seats bc already full usual as "golden week"
By air maybe booking possible but few big discount air ticket season.
More 2 days stay in Hokkaido or booking night ferry
from Tomakomai to Hachinohe or Sendai maybe comfortable.
After ferry by Shinkansen near JR station.(not ferry port side but not so far)

5 May cannot book Hokutosei seats bc already full usual as "golden week"

Hyperdia is not a booking site, so that it will show the timetable in case whether it is sold out or not. Further, it is not official JR site so that there might be some errors. In this case, Hyperdia (and also Jorudan) does not show Hokutosei because it is too early to show the timetable.

Night trains going through Seikan tunnel will be suspended for some specific dates due to inspection and maintenance for upcoming Hokkaido shinkansen.

http://goo.gl/sCgWJ3

Schedules for later days are not announced yet, so I guess Hyperdia defer the timetable for Hokutosei. In general, tickets for JR trains are sold 1 month before, so JR East will announce the date of operation (or suspension) more than 1 month before. JR East and JR Hokkaido do not announce that they will stop the operation of night trains such as Hokutosei and Hamanasu, they might scheme to stop them after the start of Hokkaido Shinkansen. Therefore, 2015 might be the last chance to get on night trains to Hokkaido.