I have two suppliers that sell that kind of Japanese papers, both in london;
Atlantis European ltd., 146 Brick Road Lane, London, E1 6RU
Tel : 0171 377 8855
John Purcell Paper, 15 Rumsey Road London, SW9 0TR
Tel : 0171 737 5199
I also believe Falkiner Fine Papers will sell them there address is,
76 Southampton Row, London. WC1B 4AR Tel : 0171 831 1151
It might also be worth seeing if T.N. Lawrence of London sell it as it is
widely used
for various ink printing techniques.
The Altlantis paper is the famous(?) Nao paper range, all totally hand made
in Japan, very good paper I am sure but NOT cheap. It cost from L50 to
L150 for 10 sheets (approx 45cmx65cm) ! The other companies prices I would
expect to be cheaper,
but it would depend what quality of paper you are wanting.
It may also be of interest to people that John Purcell sell the special
'Arches Platine
paper that is especially made for the Platinum printing Process.