Vivid colloquial. Picture reaching into a barrel of grain - 一抓 (one grab) and you pull out 一大把 (a big handful). Carries a slightly dismissive flavor: whatever it is, there's so much of it that it's not impressive or rare.
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Mirror with the opposite phrase 凤毛麟角 (fèngmáo-línjiǎo, 'phoenix feathers and qilin horns') for things that are extremely rare.