I think there is still carpet courts down at Futures level.
I couldn't find any. I looked through all the Challengers and Futures level and there's none. There are a lot of Indoor events but nowadays they are all played on hard courts anyway.
I really think it's the lack of variety of the surface is what making the top guys break all sorts of records in the Open era. Even Federer admits it in his post match interview at the AO, Federer - "Anyway, every surface is very similar today, otherwise we couldn't have achieved all these things on all these different surfaces so quickly, like him and myself." By him, he means Nadal.
Now, I don't doubt for a minute that these players, the top four, are generally very good players, but to break all sorts of records in the same era, pretty much in the same decade (the homogenization of the surface started in 2002) is another matter and this can't be done without the help of the surface and the racquet technology. It's a myth that Federer's favourite surface is fast courts. He is, in fact, a very good slow court player. This actually feels a bit unfair to the previous generations who had to play on different surfaces that varied considerably from surface to surface. I really wonder how many Slams Federer, Nadal and Djokovic would have won had the surfaces were still the same as the 90s. I personally don't give Federer more than 12, Nadal 6, and Novak 1.