#HardwareStores - It's been my experience that the smaller family chain stores tend to be great for buying nails, screws, etc. by weight, whether that's the pound or the kg. however tools there tend to be more of the 'high end' priced variety, vs. what's at the BigBox stores.
Set's of tools, say a set of wrenches, may be 'convenient', but I rarely need all of the wrenches in a set. In SAE I tend to mostly need 7/16, and 1/2 inch. In Metric, 10, and 12 mm seem to be the tools on demand/