Our way here is to know people and know what they do and what they produce. If it's a work project, then neighbors have been known to just pitch in and help. If it's barterable, then know who also is a producer. Our neighbor not far sells produce, overstock that she grows. She sets up a table with the stuff priced, and if she's not there, there's a box with change, and a note that says to leave your money in the box. My beets failed twice, so I asked for a bushel and bought that really cheap for $20. Cash. Another neighbor comes to me for their eggs and then down the road for fresh raw milk. I don't charge her, she just gave me cantaloupe, garlic, and a plate of whoopie pies. She's brought us dinner from time to time, too, and I give her rides into the bigger town to Walmart when she needs it, or the little ones to the pediatrician.
Black market is better when you know the people. So you are going to have to network. And produce something. I black market chickens, chicks, turkeys, eggs, extra produce (grapes and peppers this year), and plant starts. Also our last 13 acres of alfalfa. It's farmed, harvested, I get stuff other than money in return. I help myself to it and the straw that is stored in our roundtop that is not our straw, but it's ok to take. And the firewood that's brought, because they know we need it, and I taxi an amish girl to school on my way to dropping little granddaughter off to her school. It's also helpful to put the word out on what you're looking for.