Any question answered...

Just picked up a second hand Dura Ace FC7710 NJS Crankset.

With regards to suitable BB's I ideally would like a sealed one as I will be using this outside in all weathers. Condor Cycles said that the only option is a Dura Ace BB which do not have seals (as far as I know).

Do I have any other options?
Or is it ok to run a DA BB in the wet?

The 7710 track BB (the NJS one) actually uses cartridge bearings. The 7700 bottom bracket (which is designated as a road double BB) has exactly the same axle dimensions but uses needle/ball bearings. So although you can use either with the 7710 track cranks, the track BB is arguably better for wet weather, although both are described as 'sealed' by Shimano.

There are lots of 7710 bottom brackets being sold as 'unsealed' so I think there might be a version with the cartridge seals removed or something. I gather there is a bit of fettling that can be done to them to make them spin as freely as possible.