You could get a table mat with a measuring grid and take photographs of the object from different sides; three or more depending on how much asymmetric features the object has. Go as far away from the object as possible and use maximum zoom to get as close to isometric perspective as possible. If it’s not a very thick object, this method is millimeter accurate. With larger objects, the perspective will lead to slightly larger measurements at the object extremities: edges closest to the camera will be enlarged.

Then, in your CAD program, set up the photos as backgrounds for different perspective views.

Or, obviously, get a 3D scanner and live with the point cloud mesh approximations, it’s probably less of a hassle.

Or… just get a good set of calipers and a radius measuring tool.