You definitely cannot assume that vendors will have stock of what is on their lists, even the ones in china. Personally I think they just copy the lists with just about everything on them and a lot of vendors actually only stock the more common items, and this applies even more so to local warehouses. But a list with everything sucks people in , making them think they are a bigger operation than they really are or have been around longer, than an accurate one that makes them look smaller or newer. A few vendors do list stock levels in different warehouses and they do seem to get updated, so those might be accurate. The only local warehouse in Aus is a bit pointless with maybe 10 items in stock, and much more expensive, so that turned out to be a bit disappointing.
This is a major pain in the butt if you try to order something less popular, I think I had to try ordering from about 4 or 5 different vendors who listed what I wanted to find one that actually had it , and even then it was from a fairly new vendor I found on p.epc.h. a.t
You probably have to work out a few of the more popular vendors and try ordering from them, and buy from the vendor who actually has stock of what you want, or buy from a vendor who lists local warehouse stock levels and updates it often.