Don't know about that particular dahlia-- I think they can all be grown from cuttings-- but this is worth a try. I learned this method from plantlady2 & have never had a cutting not root. Take a small plastic container- about 2" deep & 1-2" wide, slice a few cuts in the bottom & fill with sterile playground sand. Put the small container into a larger container & add about 1" of water to the larger container. Now you have a small container of wet sand (it takes up the water) inside a larger container that has water in it. Do your cutting, dip it in rooting hormone, poke a hole in the wet sand, put in the cutting & firm the sand up around it. The cuttings done this way don't need any misting or any fussing around with- just make sure the outside container always has water in it so the sand doesn't dry out. When you get roots then transplant it into a pot with potting soil in it. You are basically growing the cutting in water- hydroponically- the sand just keeps the cutting from falling over. & before anyone says "they will rot"-- they don't. You can also get cuttings to start by just putting them in water but then they fall around & are a pain in the butt to keep from falling out of the container. Be sure you have removed at least one set of leaves & have the node under the sand- just as you would if you were doing a cutting & putting it into soil.
Ellie