Trading works for me. You can ask what they want, tell them what you want, make an offer, and they will respond with the category of good you requested if they have it.
Ive only found hunter gatherers who want livestock, though I have not been near where larger native cities should be (pueblo, aztec, inca).
I have successfully traded livestock and colonists for other livestock (that I had previously given them) people, and goods. I never asked for weapons, and was never able to get supplies.
Was able to raid and intimidate for same. Was able to make friends through raiding.
Got no benefit from bringing natives back to Spain -- was able to sell goods and artifacts for a tidy profit, but there was no novelty to returning with the tribesmen.
Also, was unable to colonize Azores but was able to colonize Greenland. I guess this is proper, as the Azores were settled just before Columbus sailed and Greenland wasnt rechristianized until the 1700s. Nice touches.