A .700 NE cartridge in my collection with Holland & Holland headstamp is loaded with a FMJ measuring .692 right at the case mouth. It would have to be .700 at the shank.
...but I'm not going to pull the bullet to find out!

Here is the blue-print for the FMJ bullet, which appeared in Joe Coogan's article introducing Feldstein's Holland double in 'Big Bore Rifles' some years back:

To buy one in the US, try the Cartridge Collectors websites. Pete de Croux (sp?) is the only guy I know of over there, not recommending him necessarily, he just sends me catalogues from time to time!

Hope this helps.