Or as I suggested previously (though I think my post may have not been
archived, so am reposting), NFL.tv (or the NFL app) is a one-off reasonably
priced purchase for an AmeFuto fan, and you don't have to run around or do
much extended research to access or acquire it. Not sure about NCAA, but
these days there's likely a similar Internet-based subscription option for
college football too...
As John noted, making friends with bartenders is always a good idea too in
Japan...
----> Purchase an NFL Game Pass 2016 subscription, whether via Web, Apple
TV (or the like) or mobile app (that you can watch on your device or stream
to a TV).
I don't do NFL, but friends do; although a very few games are broadcast in
Japan on NHK (and maybe other sources these days?), as NFL subscribers,
they're able to view any game on demand.
IIRC, NFL used to also be broadcast occasionally on GAORA and NHK
cable/satellite TV in Japan...but if I were you, I'd go with the NFL Game
Pass subscription; that way you can be assured of seeing what you want when
you want to see it, and exclude any middlemen whose access, legality and
quality control are suspect...
Personally I am a longtime subscriber to
MLB.TV, but the same holds true
(to be able to view any game or highlights, on demand,
internationally...note that if you're in the US, blackout rules may
apply...always read the fine print before purchase).
Good luck and let us know how it works out for you.