'Think' can be used as a noun, as in: "Let me have another think about it." In the case of the above sentence, the person thinks something, is wrong, and therefore has to think again. That is, the person has another think coming.
Many natives say 'somethink', "anythink', 'nothink', so that could have led to the saying in the first place. That is, it could have arisen from ignorance, or from an attempt to be cute.
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