Technically it exists here but isn't displayed in that format.
A few people have put - literally - hundreds of hours into the database and if the NGRs were listed next to mine names we'd get wholesale ripping of the data and, for example, selling it in relation to property deals, etc.
I appreciate that's not entirely helpful to somebody like yourself conducting your own research but it's the balance I have to strike between running a hobby site that people contribute to and not running a hobby site because people might feel like somewhere somebody was profiting from their hard work inputting information.
Therefore I'm afraid you only get the NGR on the mine's own page - so you can achieve what you're after, but requires more legwork.
my orders are to sit here and watch the world go by