Chartmogul is the best one I've found. There are many great ones though. You can even use open source analytics software to build your own.
Copyright law varies from country to country, but the best way recognized by everyone is to sign a contract that includes what will be used from the party that will provide you with the statistics.
Hmm .. Interesting that you say your sector isn't being addressed. Wonder why ... But if so, then that's an opportunity. I've spent the past 4 years specializing in probably THE hardest market for making accurate appraisals: the domain name industry. For me as an engineer, that has meant crunc...