Well, I finally got the hard to find P-10 battery pack for the NX. It is somewhat similar to the old P-5 for the 167MT, except it is bigger and bulkier. As Manda Yu explained on his post months ago, it will take 1 2CR5 6V lithium or 4 AA (lithium, alkaline or NiMh). The instruction manual states that with 4 Alkaline 1.5V AA you can shoot 70-180 24-exposure rolls (no flash) or 15-20 (flash in every shot).
Thanks to Taylor Kim for the information about Yodabashi.com in Japan.
Juan