If aliexpress is sold out, I hope my website can still sell normally

If a certain size of clothes on aliexpress is sold out and I move the product to my website, then this size cannot be purchased on my website also.
I don’t want that. I want all variants can be purchasable(although aliexpress can’t be purchased).
How should I set this up?
There is also a problem that variants of products that have been transferred to my website cannot be purchased(because aliexpress can not be purchased).
How can I make all variants of the website available for purchase?