Those are just modifiers to an item's price, which either have to be specifically requested by the character (used/knock-off), or applied by the GM (stolen, market flooded, etc.). The rules don't state whether or not these modifiers affect the time required to acquire the item, and it wouldn't matter in most cases -- if something costs 40,000¥, a 30% discount doesn't lower the price enough to change the interval.
Especially when you add in the off-brand factor, this should make getting an item easier. If you just want a pair of sneakers, and you don't care if the brand-name says Reebork, it shouldn't take long to find a pair. Finding something used, though, might actually take longer, depending on the item. Finding a used commlink or light pistol should be very easy; finding a used Ares Roadmaster might take a while.
Some of the other price mods get tricky. For instance, "used in a crime under investigation". This seems to imply that the seller knows the item is hot -- and it seems to me that selling something like this would be a short road to a bad rep. Then there's "market flooded". Yeah, I can see the price going down a bit, but this should also make it significantly easier to find. "Market dry" and "police crackdown" should have the opposite effect, increasing the amount of time needed to find the item.
I'm not sure how to handle the possibility that an item's on-hand, at least by the numbers -- using GM fiat works, but that requires me to decide whether or not to make the player wait. I'm open to suggestions on this.