Another easier-to-find paper that has worked well for me with an oxalic acid pre-treatment is Rives BFK 280gsm natural white hot press. A quick dunk in 1-2% oxalic, and you can get a tone like the image I printed last night. If you intend to use it for a later gumover treatment, you MUST pre-shrink it in hot water for at least 20 minutes, dry and then dip in oxalic. Needless to say, I do large batches of this paper so it will be ready. It is a really long scale beautiful paper and will print 20-21 steps on the Stouffer tablet!
I'll send you a jpeg off-list.