Reddit mentions of Itoen　Oi Ocha Green Tea,　Instant Japanese Green Tea 2.82oz

You could get that (it's the same thing) but the individual packets make it more expensive. It's portioned into 100 individual serving packets. This is Prime eligible too so no shipping charges: http://www.amazon.com/Itoen-x3000-Instant-Japanese-2-82oz/dp/B0035EPCSS/ref=pd_sbs_gro_5?ie=UTF8&refRID=1CQNPA1R5DJ81X8BWSX7

There are also several online Japanese grocery stores that carry it, but the above is the best deal per serving (once you factor in shipping costs) available on Amazon anyway.

And, don't worry about asking, how the heck would you know it came as an instant powder? That's certainly not the case for most teas! Glad to help a fellow Oi-Ocha fan get their fix :-)

Also, yea, you can totally drink it hot and it's good (though I prefer it cold). It even says on the front of the packet that you can have it cold or hot (and brew it with either cold or hot water)