Your ashtray flamingo closely matches the ones from the Flamingo Hotel opening which were made by the Will-George Co. of Pasadena, CA. Here's a link to a detailed article.
http://www.lvstriphistory.com/ie/bublitz.htm
I might suggest that you research Will-George and try to determine whether the flamingo design was custom to the Flamingo Hotel or was part of their product line. Good luck!