Hello, 

I was wondering if there is somewhere in Bangkok that has a huge selection of card / paper. I need certain colours, or at least very close to my desired colours? 

Most stationery stores have limited colour ranges. 

And, also any companies that can make stylish boxes/packaging to spec. 

Kind regards
 

Try the big book stores in the malls. They usually have all that sort of thing.

B2S was the place in Chiang Mai and there are some in Bkk.

Office mate, they are in many locations.

B2S and the stationery department in Robinsons have a good selection. 

There is a terrific stationary store in Phra Khanong: "King Tong Stationary", just a few steps from the BTS station.  This store is stocked in depth with paper and art supplies.

On Sukhumvit at the corner of Sukhumvit soi 44/1.  From BTS, Take the lift at Exit-2 to street, walk in direction of traffic past the condo tower, next corner.