Good morning, Auckland...and welcome to the forum. Going on these pics I would say that you have an original Luftwaffe Observer's badge by the maker Gebrüder Wegerhoff, Lüdenscheid (GWL). And yes, you are right….GWL pieces are highly sort after, and can be expensive…but it’s all about condition. The missing reverse hardware is going to seriously affect the value. That having been said, It is a piece of history and I’m sure that you will have no problem selling it. So, dealers, forum sales sections (such as ours), auctions sites (military). An internet search should bring up some options. For comparison, here is an example of a complete badge by the same maker.