I have found a satin paper from
Mediatech in Montreal, Canada, that has a great surface, slightly finer or flatter than the HP paper in a 44 inch roll. Works great with my Z3100..
It's called Satin Photographic Paper "Instant Dry" 10 mil. # JPX-PDQL comes in 44" x 90 feet also 24" , 36", 42", 50", 54" and 60"
they have lots of other kinds of paper as well, they specialize in paper for large format printing... Mostly commercial applications, it seems. Everything is house brand... but I'm impressed so far. You'll have to call them to get information or a swatch book.
cheers,
Paul