Hi Eric,
It's the IMTRA ILSH60150 "Venice" lamp and I'm not finding it on the Defender site now, either. On the Imtra site it says, "Sold Out" - Note: only available while supplies last" and in an earlier post Richard May said it was discontinued and we all may have to look for a different fixture. What a shame as it's the perfect replacement. 

Craig Briggs - s/v Sangaris / SN68  Tropic Isle Harbor, FL