My experience has been the same (frustrating) trying to purchase from even local manufacturers to sell online has been a complete failure.
Failure 1: a great miniature train amateur wanted to sell his high end creations. After selling $5000 / year for him he decided he didn't want to sell to me anymore. He has now opened his own web site.
Failure 2: A computer recycling plant wanted to sell pulled parts to me. Management changed and the parts (mostly motors) are no longer being pulled, printers are being shipped directly.
Failure 3: A candle manufacturer wanted to sell to me wholesale. Whenever I sold a candle, it wasn't in stock (they had to make it) lead was 1 to 5 weeks - too long. Then they sold the company and it was impossible to get. Had to refund clients.
Failure 4: A local manufacturer makes recycling bins for institutions. I politely offered to sell their products. A year have passed they have not responded. They implied that they already have a web presence and somehow my presence would hinder their efforts.
I have grown frustrated in approaching individuals, companies to offer my expertise in selling stuff. Now, the best combination (for me) is to keep doing what you do, if you buy special stock for building your products - why not break the lot and sell that / unit. Example: I make and sell safety widgets but I buy the safety tape by the case (600 meter) why not sell the safety tape by the yard too? - I do that.
Simply put, if you have something on the shelf for your own use, which you use all the time for making your widgets, sell that item too by the foot or dozen or unit. You may get a 10 fold profit margin by doing so.
What is most frustrating is that you depend on the success of those places to succeed yourself. If they decide something which may affect you, you have very little say.
This approach makes a slow but stable growth for me and I do not have to sell millions to make a salary. For me it is manufacture, and sell retail. Profit margins are really good and it is possible to get a decent - stable - salary.