can someone tell me a paid service to check cd sales in america?

I want to check cd sales of some of my artists that were sold back in the year 2000. What do radio stations and artists use to find this out? Is it called mediascope or sumthing? I want a paid service. It has to allow to find cd sales back in the year 2000  in american though. can you list all the paid services you know please.

Thanks