p179 of ATGET:Modern Times, vol 4 of The Work of Atget, John Szarkowski
and Maria Morris Hambourg, MOMA 1985 has a note on Atget's prints.
It states he used several papers at different times. They were albumen
and matt albumen papers rather than normal POP. And they would all have
been gold toned.
I don't know if albumen paper is still available commercially - it was
made by The Chicago Albumen works a few years ago. Atget's techniques are
probably those given in any photo text of the 1890's or so when he learnt
- he was not given to innovation in the darkroom. The reprints by Joel
Snyder and Richard Benson on CAW paper from the originals were very
similar. You would need also to start with similar negs to get similar
results. He used glass plates. Most photographers at the time gave very
generous exposure and development by our standards. Again it might be
worth looking at contemporary literature if you really want to acheive
similar results.
Peter