There is a UK body which is an association of organisations in the environmental sector called the Renewable Energy Association. They have a very comprehensive UK-based members' list and links to all the major associations representing the interests of individual segments of the environmental industry. It has a very flexible search facility.
Similarly, there is a UK association that covers the Wind and Marine engergy sector, RenewableUK, which has a very accessible List of Members complete with links, addresses and contacts.
The Green Pages website offers a global list of companies involved in environmental activities. It provides postal addresses, email addresses and website links.