I have a spec C roof vent. It's been so long, that I can't even remember where I got it. Maybe eBay from outside the USA.
I bought it for my 2000 RS. After seeing the pics of the coming 2001 Impreza, I bought my 2000. The only bad part, I had to get a sunroof with the RS model. So, I ordered a base-model roof from Subaru, and put it in storage to install later.
They don't sell these any more?