Jacquie,
If the dress has a plain jewel neckline, you can make your own mandarin collar. Here's how: Measure from the center back to the shoulder seam around the neck. Record this measurement, because you'll need it again. Add to that the front neck measurement from the shoulder seam to the center front. Remember that most patterns these days don't show the seam allowances, to be certain that you're measuring to the seamlines, not the edges.
Draw a straight line on a piece of paper for these combined measurements. Draw vertical lines at both ends 1-1/4 inches up. Now, this line can be higher, but might be uncomfortable. Label the left end CB for the center back. On the first line drawn, put a dot from CB the measurement of the back neck. Draw a second long line to make a rectangle. Slash the pattern at the dot. Keeping the lower line the same length, raise the rectangle until the CF is 3/4 inch from the original position. (I usually just draw a long line, then put the pattern on top of it, and raise the front 3/4 inch from the line. This will shape the lower edge, and make the top edge slightly smaller. Now, curve the front edge to make it into a rounded shape for the mandarin. Add seam allowances. You're done.
Teri