If you are planning to go to Tokyo to buy some clothing, here is some advice on where to go to find gyaru inspired clothing.
Firstly, no shopping trip to Tokyo in fact Japan, is complete without going to Shibuya at least once. It is quite easy to get to Shibuya, this little suburb in Tokyo is serviced by more than five separate train and subway lines. Once you arrive at Shibuya, take the hachiko exit. Immediately right in front of you is the famous Shibuya crossings. Once you make your way to the crossings and look straight down the road you should be able to see a really tall building called Shibuya 109. This building is the premier shopping complex for anyone who wants to buy gyaru fashion. There is almost 7 levels of non-stop shopping here. Although gyaru fashion magazines and their models source the majority of their fashion from the stores in this tower complex.
If Shibuya is a little bit too hectic for you, then I would personally go to Harajuku. This train station is only one stop before Shibuya. The shops in Harajuku are spread over a wider are, as there are no department malls. Instead you will find quaint little shops tucked away in alleyways. You will find a lot of boutique gyaru shops just by doing a little bit of discovering. I recommend that you start off by heading to Takeshita Dori which is accessed directly in front of the JR in Harajuku station.
There are other places where you can also get gyaru fashion however I found that Harajuku and Shibuya had more than enough shops that it took me two days to see everything that was there. If you would like to find counter fashion that is more appropriate for an older adult then I would suggest you check out one of the peak department malls such as Marui.
If you are in Osaka the easiest place to find gyaru inspired fashion is a Amerika-Mura and Shinsaibashi. The department mall called OPA is the closest thing to Shibuya 190 in the west of Japan. When I was in Osaka a couple of years ago, I noted that the gyaru fashion there was a little bit more laid-back and mature. If you want something that screams out a little bit more personality than Tokyo will have a boutique shop to fit your needs better. If you are into hime gyaru or Lolita fashion Harajuku has a better concentration of boutique shops.