Agfa is out of business, but Brovira papers can still be found cheap on eBay.
ISO for paper is somewhere around 10, so you will need long exposures. The Polaroid 350 is an automatic camera, which lets you set film sensitivity from ISO 75 to 3000, but has no manual shutter or B setting, which probably makes it unsuitable for what you plan to do. Also, you will have to reload your camera in the darkroom or in a changing bag after each shot.
Maybe you could fool the camera by taping off the "electric eye" that controls exposure, leaving only a small hole to let some light through. You will have to experiment to get it right, if it works at all. Remember that the maximum exposure time on these shutters is 12 seconds. Why don't you try some outdated (=cheap) Polaroid packfilm first?
Oh yes, don't use multigrade paper: the color of the object photographed will influence the contrast, especially if you have greens and blues in the shot.