Tough question. It’s kind of like sending him to NYC and asking him to buy you a watch, and asking us what you want?.
I’m not aware of any kilns in Tokyo, but the
Ueno Green Club is there. Your best bet would be to give some parameters:
1. Price range
2. Size (go for small for transport)
3. Glaze color, or unglazed
4. Then a general guide to help recognize some of the makers’ stamps.
http://www.tokoname.or.jp/bonsai/maker-e.htm
https://japanesebonsaipots.net/chop-and-signature-resource/
If you really like Koyo or Ino, for instance, send him some photos of good example pots you’d like, and their chop marks. I suspect these 2 makers and many others are much cheaper in Japan than here. Good luck!