Source?? This is a non-Biblical assumption. Meaning, we have no idea if in fact, it was something a rich man wore, or if it was Jesus' only possession.
Maybe his mother or aunt made it for him. Or maybe one of the women who followed Jesus and supported his ministry gave it to Jesus, knowing that many times, "He had no place to lay his head."
Israel gets cold in the winter, and even snows in the mountains. So, a good warm garment is essential for someone who was constantly going from Jerusalem to Galilee and back.
You have just held up Jesus as a rich man because of his chiton, or robe, when Scripture is silent on why Jesus came to have this garment. That is called being extra biblical, which is a typical tactic of Word Faith people, who don't know their Bibles, and only listen to the lying evangelists who try and get them to donate more, with this unbiblical nonsense. And only the preacher is getting rich!