Call Motor Trike they have them. They mount to the fender with bolts,,, not my preferred way. I made mine and a bracket. You will have to get under the rear and design a bracket for the Adventure. Mud flaps can be made easy with combine belting from Tractor Supply.
I went through all the searching back in June of this year.
I finally bought a set of heavy duty truck mud flaps and cut them to fit and then glued them on with Marine Goop. Still holding great and cost a little less than $20.00 for the flaps and about $3.00 for the goop.
Mine are not fancy and don't light up but look pretty good if I do say so myself and they work.
you can get mud flaps from the trike shop and they work great does takes a little work . You just turn the roadsmith emblem forward & roadsmith does not show.....( motortrike people should love that. lol ) easy to make work on a motortrike