I am an importer and the first thing you need to do is find a freight forwarder (here in Aus) that can handle your shipments.

You will not find any factory in China (or in many countries) that will ship item per item, they may agree to a pallet consignment, but even then it is really not worth thier while. They WILL require payment up front.

If you use Air (which may be cost prohibitive)  you can purchase less that way.

For bulk shipments, unless you are bringing in a container (smallest 20'GP) most factory's will not be too interested.

A consultant company will cost out to US but they charge a hefty fee, and duty will be payable for any shipment over $1000 AUD.

A forwarder can advise you of vessels avaialble to take consignments but you usually need to buy in bulk.

If you are talking about drop shipping - which a lot of eBay sellers use, someone else may be able to give more information.

If you have dealt with the suppliers for a long time, they may be able to offer alternatives from thier end, so best to speak to them when you are there.