I am guessing that the group really means blocks that will finish up 9" square, which are 9 1/2" with seam allowances.
Any block that is based on a nine-patch will be easy to make into a 9" block.
Another sneaky trick is to buy a pad of 6 squares to the inch graph paper. Copy any 6" block onto the graph paper, then enlarge it to 4 squares to the inch graph paper (counting the squares to locate the lines) and you have a 9" block. If this is too mathematical for you, share it with your group and maybe someone else can do it.
Good luck!