Perhaps a 1-of to tutor for it? Well it can be sacced to Forgemaster too if it comes to it.
Rarely will that be a good idea, because in the matchups you sb grave hate in, you're gonna need it to stick.
Also, what happens if my opponent has a Cage in play, then I Forgemaster for Phyrexian Metamorph copying a Non-creature artifact, let's say a Tangle Wire (assuming I have 1 in play and the rest in the graveyard and that's my only way to win), would that play be legal?
No. Metamorph is a creature card in the library, so it can't ETB. The ETB replacement effect happens as part of the ETB, which Cage stops.