I know Japanese on very elementary level. It is also not my mothertongue.
Google translator give no or little to understand japanese. Usually it gives gibberish.
I prefer to use dictionaries like Denshi Jisho - Online Japanese dictionary for basic words and eow.alc.co.jp and others for advanced.
Also I have got japanese friends and I ask them for help with translation.
Have you talked to actual sellers of stones not via email, but rather in person??
I do not think the kanji means Mejiro, and koma is not the finest nagura. Naguras vary in quality just as any other Jnat.
This piece could very well be a Chu nagura, which is very common