I got 28 Brass Nuggets from gardening: A bag of Tree Cutting + Fire crystal + Fire crystal in an Earthen Flowerpot. If you need some in the future it might be an investment worth looking into.
ahh... so this is how to make them... by using some tree cuttings in a brass pot... I have always thought that I could get them by killing some monsters
But I must add: you still need a zinc ore to make ingots. 6 brass nuggets replace 3 copper ores in this recipe. Therefore, brass nuggets = waste of time, BIG waste of money.
Only use for these I can see is to bring them along while mining somewhere that yields a lot of zinc, so you can compact your ores into ingots on the spot. These take up less room than copper ore.