Hello cyrilp,
You can open Tools Menu -> Mesh -> View Mesh UVs dialog and manually export Occlusion and Normal map to a file from the corresponding tab of the dialog.
Also some formats, for example, FBX, automatically saves original texture and normal map, if present, providing that "save texture" option has been enabled in the Export Model dialog. So you'll get {model}.fbx, {model}.jpg and {model}_normal.jpg files on export.