The LW Experten board has been replaced by
http://luftwaffe-research-group.org/index.php - about two years or more ago. If you remember your user credentials to the old board you may still be able to get in. The lwag.org still appears to be active, though I haven't been there in a dog's age.
There are number of titles that cover the 'Blitz', the best being 'The Blitz, Then & Now', all of 3 volumes. Others may have better suggestions.