Well, you could look at Home Depot for a plant stand on wheels. One of my students uses this to wheel around her harp and it works great. She did have to secure the stand around the feet with a bungee cord, but she pooled some fabric around the base and you don’t even see it. Was this what you were thinking? Other than that, all that keeps popping in my mind is a dolly of sorts, maybe a half-dolly you could disguise/cushion with fabric. You’d still need to figure out a way to secure your harp though. Home Depot would probably have those too.
Hope this helps 
Karen