I’ve personally never heard of TB500 and itchiness.
I think BPC-157 in combination is so popular because they really work so well together as a synergistic duo. There’s tons and tons of anecdotal reports of using the combo to heal injuries or prevent injuries.
I’m not sure what you’re asking by if it’s the same at each vendor. Most vendors will offer BPC157+TB500 blend but they will also have other blends like GLOW and KLOW which include other compounds as well.
So if you want to improve your BPC-157 effects then you could try researching one of the blends.