My local Jusco is now full of them, different sizes, colours and very different prices!!!
Under 3000yen gets you a basic set of 3, 1m, 80cm, 60cm, with a 1m streamer flag, pole and spinning wheel on top!
60,000yen gets you a whole lot more!!!!
There also a whole load aimed at catching the kids with cartoon characters on them.
For a few hundred yen you can get little sets of Koinobori.
Whilst I was in there the other day looking at them I can guarantee every kid that walked past exclaimed 'Koinobori!'.