Wait... which phaser are you looking for. The MR one was the boomerang phaser from First Contact (as well as
DS9, Voyager, Insurrection) the dolphin phaser is the one from Nemesis.
For a boomerang phaser you can just get a Playmates phaser and modify it, or find a resin kit.
The boomerang would probably be the easier route to go. You can still pick up quite a few Playmates on Ebay.
If you really want a dophin (I can't imagine why. Personally I never liked the design of the Nemesis props, but to each their own) they do seem to be getting fewer and fewer. All I can do is suggest Ebay and the Junkyard and wish you good luck.