@ Cuhan: Yes I know the sage Naruto will be limited to 100 pieces. I have my contacts to help me find one if needed.
No convention. As far as I know, with these kind of lotteries the tickets will be scattered over the local stores in japan where you can buy one to possibly win a unit. It´s very similar to the yearly Ichiban Kuji lotteries.
The only way too get one probably, is by searching on (japanese) auctions or visiting one of those shops that sell collectables handed over by the customer. In other words, you have to be very lucky.