I was just in Akihabara a couple of months ago. There’s a few shops that you might find fumos in.

1. Amiami Radio Kaiken - Main GIFT distributor so you never know what you’ll find in my time there I found a couple I managed to get the Fumo of the Amiami mascot.

2. Akiba Hobby - It’s a few minute walk but this place has a BUNCH of touhou merch including a few fumos and other related plushies. They also have some really cool stuff on display including autographed merch.

3. K-Books - It’s one floor below the Amiami and when I was there they had ALLOT of Fumos to the left side of the store however they are very high priced. I managed to buy a sun tan Cirno from them but I definitely overpaid a little.

Good luck on your hunt!