Parts needed for A/C installation

Being an aftermarket add on system, finding parts is more difficult.
Dryers are basically the same functionally, you just need to find one with the right fittings. Same for the expansion valve. The original valve could still be in working condition, you won’t know unless you try it. You could try Classic Air or Vintage air for parts. There are other vendors folks talk about on this site, you could search some threads on here.

I don‘t know how familiar you are with ac work (I am an amateur), but you will need to evacuate the system prior to charging it.