It's entirely dependent on the maker of each custom apparel. They can restock it with a custom apparel token if it's sold out, or they can choose not to.
is it rude to dm them and ask them to make more so I can get some kitsune tails in a particular color? When they have time and moonstones obviously and maybe shoot me a heads up for it?
I did and I offered to pay full price for it if they decided not to and just had a couple spares. I even offered collateral if it was a payment plan. I don't want to stiff anyone ever so yeah that doesn't constitute begging I hope