Yes Ben by all means ask him if you see him.
There are these on ebay at the mo. http://cgi.ebay.co.uk/RAF-C-TYPE-FLYING-HELMET-early-type-replacement-earcups_W0QQitemZ250370656733QQihZ015QQcategoryZ112473QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
These are identical to those that are on my early pattern C type, which are just stitched around the base.
There are also these http://cgi.ebay.co.uk/RAF-C-TYPE-FLYING-HELMET-late-type-replacement-earcups_W0QQitemZ250370656720QQihZ015QQcategoryZ112473QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
which are the type that feature on some D helmets, and are stitched around the base of the cup and around the edge of the flange.
Chris, You mention a lip around the base. There is a third type of cup which comes as a complete unit of rubber earcup and donut. This is attached straight to the helmet by gluing and then stitching the donut to the inner chamois of the helmet. I'm not sure if my mate has any of these or if anyone produces them. As below:
I think those on ebay shown above may be the same as my mates (although he isnt the seller) which as mentioned, and shown, are not only molded from actual examples but are also accurate.