Ebay won't let you do it because it helps scammers who buy the bags to make their fake items seem authentic.
I buy my bags preowned these days, and sometimes I don't get a dustbag, annoying as that is.
I need a place I can find dustbags.
I used to buy dust bags from eBay when I bought bags from Coach outlets. It is stupid of eBay no longer allowing people to sell deisgner dust bags. Anyway, if I need a dustbag for a bag, I'll just use a pillow case.