The difference in the hat options is due to the fabric content. When selecting your hat, double check to be sure that the hat matches the same cloth as your ASU.
The fabric differences are best explained through this link below.
https://www.marlowwhite.com/army/uniforms/fabric-types.html

The size chart on the web is geared toward male service caps and berets. The female pot hat is a different design and therefore sized in half-size increments. Being a 22-3/8, you will want to order a 22.5 hat. The good news is that almost all of our customers find a very good fit with the ½” increments. We’re happy to assist with any sizing questions you may have before making a purchase.

This hat is Midnight Blue. We no longer carry anything for the uniforms that have been retired such as the greens. You could try checking with a military surplus store or historical uniform organization to find the hats previously used.

Good question! Try watching this little video on how to measure for a cap.

http://bit.ly/2iMitl1

Have a good day!