Better off making your own. Find some 'weeds' that are growing vigorously. Pull them up and fill a 5 gallon bucket full. Fill the bucket up with water and put a lid on it. Let it sit outside in the sun for a couple of months. Then strain out the plant matter, and add 10 parts water for every part liquid fertilizer. So 5 gallons makes enough for a 55 gallon drum. Then just spray it on your plot. Leave a strip unsprayed so you can see the difference in a couple weeks
Weeds like lambsquarter, pigweed, marestail, ragweed, and dandelion are excellent for this. Now I also use things I grow specifically for this purpose, like comfrey and borage.
The best thing about this is that you don't just get the NPK, but all the other stuff too like calcium, magnesium, sulfur, zinc, molybdenum, etc.