Marko,
Awagami Masa paper. Machine made, sulfite pulp, BUT a very nice and cheap (~USD 1.2 per 21x31" sheet) paper that works great with every iron / iron-silver process I know. Very bright (and almost cold) whites, very smooth surface, clears very quickly, very nice dMax (best of each and every paper I had tried before it). It's pretty thin though (~90 gsm, but quite strong for that weight), not advisable for big (> 30x40cm) prints. (Paper is cheap, therefore shipping from the States isn't much a problem; I ordered three 100 packs of this paper before...)
COT320 is great BTW - even if it doesn't give as good dMax as Masa does... My third choice after Masa and Weston Diploma Parchment. (Pity that Weston isn't a little brighter - too warm for many tastes...)
Regards,
Loris.