I have found that almost all of Nirad Chaudhuri's books are still available in Indian editions. That said, I must add that those editions contain misprints and typographical errors which can be annoying. The print quality also could be improved, but I suspect that the problem is exacerbated by the type of paper in use.
Here are some resources that you can try.
The Stanford Bookstore also carries a few books by Nirad Chaudhuri and his son Kirti Chaudhuri.
If you are in desperate need of a particular book, I would also advise you to search for it on any of the search engines such as Alta Vista, Lycos or Excite. I have seen several books up for sale.
To find materials on Nirad Chaudhuri, just type +nirad +chaudhuri in the search field.
If you have access to the Lexis-Nexis database, you can find a number of articles and features on Nirad Chaudhuri. I use the version available to the Stanford Community.
Among things available on these sites are interviews with Nirad Chaudhuri, reviews of his books as well as an obituary report on Amiya Chaudhurani.