I have gotten a ton of free replacement covers from BBC/WB no problem. I had some spillage on my whole collection of AYBS? dvd's and they sent me 12 covers free of charge, even free shipping. Another company, i forget which one, makes you send in the whole DVD w/ cover and they will replace it. Just go on the respective company site, email them or call their consumer hotline and find out their policy on cover replacements.
there are a few sites like spittie.dk and cdcovers.cc but its prob not what you are looking for.