The IFC sketch comedy show has attracted many high-profile guest stars in its three seasons, including Kyle MacLachlan, Aimee Mann, Roseanne Barr and Andy Samberg.
In an interview on CNN, Brownstein admitted that efforts to secure a cameo from The Hobbit's Blanchett have been unsuccessful.
"A couple years in a row we've tried to get Cate Blanchett, which is crazy," she explained.
Brownstein added that she would also love Grizzly Man director Werner Herzog to appear in one of Portlandia's sketches.
"Werner Herzog, the director, we have tried to get on the show," she said. "There is always this pie in the sky list, but each and every time I feel happier and luckier with the guest stars that we do get, so I would consider them dream casting as well."
The star concluded: "At the beginning of the year you think you are going to end up with every Oscar-winning actor or actress and that's not usually the case!"
Fred Armisen recently admitted he is surprised that Portlandia has found such a devoted audience in the last few years.
The series airs Fridays at 10/9c on IFC. Watch a clip from the show below (US only):