Tanaka Works is one of the many major company's in Japan that make hobby replica weapons and accessories in both airsoft, and plig fire cartridge/blank fire guns. Some of thr other major ones include Craft Apple Works(CAW) Maruzen, Tokyo Marui, and China based S&T. They make replica of Baby Nambu's, Type 89 Grenade Dischargers, and most of the Arisakas to name a few. A lot of the replica/reproduction accessories ment for their replicas are not exported widely outside of Japan, so it's not uncommon to mistake them for either the real thing or a blatant fake, which they are really neither. They've tricked people a few times on this forum before with auction site listings in Japan.
For what it's worth their craftmanship is very good, and I would have no issue using one on a shooter Nambu for fun.