I have not heard this expression either. I am a native to the East Coast as well. "Take a seat" and "Grab a seat" are both used as an expression to sit down. Pews are only in churches, and do not have the same meaning as seat or bench.

I have never heard it before, and I am American. I am from the east coast, so it is possible they say it in other parts of the U.S..

No, it's not used here. In fact, when I saw the question I was completely puzzled as to why one would say this. A pew is bench seating in a church. So it made no sense to me.

This is used more in British English. This is a colloquial expression which means takes a seat. It is still said these days by mainly the older generations.