We have five days in NYC and are hoping to spend most of a Sunday at Flea Markets. Does anyone have suggestions on where we should go? I am more into collectibles than tube sox and knock offs. We will be staying at the Inn on 23rd.

There's the Chelsea flea market at Sixth Ave. and 25th.

I also like the flea market at Columbus and 77th, although that's not as close to you. That has both an outdoor and indoor section -- you might be more interested in the stuff inside (it's held in a school.) What do you collect?

The Chelsea Flea market is a short walk from you and has the collectibles you're looking for. Go early (8am) with coffee in hand. There's also a newer one I've never tried on west 39th b/w 9th-10th ave called Hell's kitchen flea market. I hear it's not very large but prices are cheaper than Chelsea.

You should also check to see if there are any special antique shows going on while you're in town.

There used to be one every weekend on 24th just a block west of Broadway. But I don't know if it's still there as that was a couple of years ago when I was commuting regularly.

I saw on Fox News, Channel 5 mornings that the street fairs in NYC start up again this weekend. I think there's a fair at Astor Place and at Waverly place this weekend. Not sure whether they are Saturday or Sunday.
But Astor Place isn't very far from 23rd street. Just walk down Broadway through Union Square until you get to Astor Place.