Buying a folding bike bag

I'm currently living in Tsuruhashi, Osaka. I've just bought a very nice folding bike and I'd like to buy a bag to put it in when travelling on the train. I've seen them on Amazon Japan for 10.000 yen, and on Amazon US for thirty dollars. The problem is that kind of product cannot be delivered to Japan by any Amazon outside Japan (sports goods import is restricted) Due to the high price difference between US and Japan bags (same models, double the price) I would like to ask if anybody knows a shop in Osaka that sells folding bike bags at a reasonable price (around 5.000 yen would be ideal)

Which type?
If means "carrying bag" under 5000Y exist.
TOIGA product very famous reccomend.
http://tiogajpn.com/products/carryingbag/top.html

Carrying bag is "輪行袋/Rinkou-bukuro" in Japanese
or more simple calling 輪行バッグ/Rinkou bag
輪行 means carrying by public transportations.(train,bus/taxi,airplane and ferry)

How about Rakuten web?
http://search.rakuten.co.jp/search/mall/%E8%BC%AA%E8%A1%8C%E8%A2%8B/?f=1&s=4&max=4599&min=3400&x=0
http://global.rakuten.com/en/search/?k=%E8%BC%AA%E8%A1%8C%E8%A2%8B&sm=...

They have these in larger Bic Camera & Yodobashi Camera stores as well as bicycle shops. Have you tried any of these shops?
http://www.kinkicycle.com/p/bike-shops.html
My knowledge is much more Tokyo based, sorry.