This is going to sound ridiculous, but when I was a teenager in the 90's I had deep red walls, Korn posters everywhere, and hanging from my ceiling was a large 4 foot plastic skeleton that my parents bought as a halloween decoration and I kept it in my room all year, hanging by a rope, of course. I also took the covers of all my CD's out of the cases and I had one section of a wall where I taped them up. I used glow in the dark paint to put pentagrams everywhere so at night my walls and door lit up. looking back, I was pretty strange.
Anyways - for a "grungy" looks, I would recommend dark gray walls because it works as both goth/grunge style and yet its modern now so if you change your room again in a few years you can easily do so, gray will work with anything. Lava lamps are always 90s. Posters and magazine cut outs as decorations are also very 90s.
If you're looking for specif decor, you can always try sites like Etsy or Society 6, you can buy grunge styles of pretty much anything on those websites!
Hope I helped.