The phrase should be "then you've got another thing coming".
Grammatically, probably, yes, but then it wouldn't make any sense. It means that the person thinks you
should think about it again!
The phrase nearly always starts "If you think....", so logically it follows that the rest of the sentence will be about the "thinking" process.
If you think I'm ever going to date you, you can think again!
If you think I'm ever going to date you, you've got another think coming!
It's true that "think" is not a noun. The noun is "thought", but the phrase uses "think" and it has been the same as far back as I can remember!
We use it as a noun in another phrase that I just remembered.
Q - Where did you leave the car?
A - Hang on a minute, I'm just having a think about it.