Most of them, no, I'd imagine. For something like HGH or hCG, you can get with a prescription, but due to the many health benefits and performance enhancing/anti-aging attributes of HGH, you'd have to be SERIOUSLY deficient in order to get a script (either that or if you have a decent doc, he may offer to write you a script but you'd have to pay out of pocket, in which case, you're gonna pay and arm and a leg for it!).
As for PT-141 (aka Melanotan), I think it's still in clinical trials (but I could be wrong; been awhile since I researched it). Though, in the future, if you see XX-### (in other words, a few letters followed by numbers) that typically means the given compound it still in research phase and not yet available, at least via prescription. The letters typically abbreviate the company responsible for the compound's development; like, for PT-141, the PT stands for Palatin Technologies.
However, if you are interested in this or other peptide compounds for research purposes, they can be obtained at very affordable prices through several of the board sponsors. Personally, I recommend Genesis Peptides, which I currently use. The quality and customer service are unbeatable!