Have you tried going to these vendors directly to dropship? I assume you would get big savings cutting out 2 middlemen. Most suppliers aren't properly setup to dropship but would probably be pretty easy to get an account with a bigger discount without white labeling, at the cost of having to do custom integrations.

There are certainly faster shipping options from HK and China that aren't overly more expensive that you could get them to use or provide your own account given enough volume.