Hi Luke and welcome to the forum,
You can search for wholesalers in our directory of fully verified suppliers Link hidden: Login to view, just use the search engine to refine your search as required.
In regards to Amazon friendy, and US based wholesaler should be ahppy to send your shipment to any US address, including the Amazon FBA warehouse. In regards to margins, with wholesale it works on purchasing volume. So essentially, the more of an item you purchase, the bigger your wholesale discount will be (within reason of course)
So just speak to your supplier/s about their stucture in regards to purchasing to see how much discount you are able to secure.
Cheers