Out of curiosity, I e-mailed Aqua Signal.. They were kind enough to reply, but it is as suspected..:
copy of letter from the USA rep..
Messmer, Matt
8:16 AM (2 hours ago)
to me
Hello Claude, unfortunately we do not offer the lens only anymore. It is more cost effective to produce the entire fixture which is brought in from our overseas factory.
The good thing is you will get an extra lamp, and the suggested list for the entire fixture is $32.95. The part number is 25100-7 and I see Defender has it for sale for $28. You can also try West Marine as well.
If you should have any other questions, please let me know.
Sincerely,
Matt