The short supply of PoE stuff is not new, it's been that way since April-May of this year when it became obvious this wasn't going to be a couple weeks or a month long ordeal, but was going to go on for some time. Many vendors bought up hundreds of PoE injectors at that time, I know we did.
I am confused what you are trying to do here... If you want to use more than one phone on a single bridge, get a small PoE switch, you can usually get 4-8 port PoE switch for less than the price of a few injectors and then it will be much simpler. Also, do not chain phones one behind another, power supply or not, it can cause odd behavior sometimes.