Selling on Yahoo Japan Auctions is probably your best bet. However, finding new cards for your collection is harder, as you need to find someone selling them on YJA, and then outbid everyone else for them. I do see VG cards listed every so often though. They are frequently listed alongside VIPER and other Takahiro Kimura stuff.
Sites like Suruga-ya might also deal in them. I don't know if there are trading card shops in Japan, like teleca.net exists for telephone cards, but likely.
There could also be people here interested in them, if you took some photos and attached to the thread.