There seems to be a serious lack of decals for 1/72 Great war kits (in fact, in comparison to other scales, there's a distinct lack of kits, too). I don't really know what to suggest- if you go to
www.hannants.co.uk you may be able to find a sheet of 1/72 German Cross motifs of various sizes, but I've searched the site extensively for any kind of Greta War Aircraft Decals with not much joy (For example I wanted a replacement set of Decals for the Revell 1/72 Sopwith Camel, as the ones that come with it are REALLY awful, but the only ones available are the "Colourful Camels sets 1 and 2). Failing that, you could always paint them- and I saw somewhere (WW1 modelling site, I think) a novel way of printing decals osing a colour printer and attaching them to the kit, but I guess that would only really work on a larger scale.
Looks like a paint-job- I hope you have a steady hand.
Still, it's nice to see another 1/72nd modeller- Good luck!!!