I have no specific knowledge of this, and I doubt that it would be easy to come by. Here are my quick thoughts on the matter, though:
If I were a hardware vendor who wanted to start selling a few DIY supplies, I would probably inquire to a DIY e-liquid company as to what they would offer for wholesale prices for differently-sized bulk orders. I believe that this is a fairly common practice, and that it benefits both parties. This does not require very much initial investment, other than the cost of the bulk orders.
If I were looking to seriously compete with said DIY e-liquid company, then it would not make sense for either party to enter such an arrangement, and I'd be looking to source the individual chemicals from as close to their manufacturing level as possible, and mix them myself. This would likely require a lot more initial investment for the proper equipment, possible licensing issues, and many other things.