Searching for keyrings

Hello,

back in 2007 in Akihabara if I recall I found keyrings with the shape of station banners, let's say for example Kanda station with Yamanote line green and white banner, unfortunately my keyrings were lost or broken, so I'm searching for new ones since I will go to Japan, do you know any shop or place where I can find them?

Model railway shops
Railway themed shops
Railway museums
Even some regular tourist shops

Depends where you are travelling to which option works for you.

Official railway goods including keyrings are sold at online shops of that railway company, as well as inside train stations that belong to that company. If you have a specific design in mind, you should either go to their official website or ask the railway company or a train station.

For example, when I lost my Tokyo keyring, I recall asking at a random shop at a Tokyo train platform in the suburbs. The shopkeeper suggested I go to another, actually, smaller shop, because they usually have more stock, and she was right.

The following official website is just for your reference.
https://www.jreastmall.com/shop/c/cD401/

I've seen keychains like those for JR lines (like Yamanote) before in Tokyu Hands, but I'm not sure if they're always in stock. The kiosks (the stands selling snacks and drinks) on the the platforms inside the stations would also be a good place to check.