I have a startup clothing company that could be much larger if it were a joint venture with another company with more experience and know-how than I have. How do I make appointments to discuss this with name-brand companies?
That said--I have to play devil's advocate here and ask a few obvious questions:
If you can come up with viable answers to all of these, and if you've invested in professional renderings of your line, along with samples and other professionally developed marketing materials, then go for it!
To get started, visit their websites and do some research. All these companies may have info posted online about how to approach them with new ideas. If not, you can still get the phone numbers of the main headquarters. Call and ask to speak to the VP of design and/or the VP of marketing.
Even if you can't get through to the people you want, you should be able to speak to someone there who can tell you what the process is, or an address where you can send your materials. It's important for you to get the lowdown on how to do this correctly, as I suspect all these firms may require legal representation or have other formalities in place when discussing new concepts, products and partnerships.
These processes are created to protect your ideas as well as future claims against them, so it's important that you follow their directives. In addition, before you try to set any appointments, do whatever due diligence is needed to protect your copyright/ownership of your line(s), design, products, etc.
Best of luck!