Strangely I founded how to create patches for Session Horn and Session Strings, but Instruments like French Horns in Orchestral bank of Logic (for exemple), I can't find how to make a patch with it. It doesn't appear in the list. Do I have to choose a special thing? Sorry if that seems simple to you but I am new to Mainstage, and not so stupid, but obviously there is something I didn't catch... Thanks I use 3.4.1 version.

Hi - The French Horn(s) patches are definitely in there—you should be able to use the standard method for creating/adding a new Patch (Edit mode; "+" button; select the Patch in the Patch Settings pane). If they don't show up in the list under Orchestral (as in the screenshot below) maybe check the Sound Library Manager (under the MainStage menu), and try reloading them..

Thanks Joe. It doesn't work the way you show. I don't know why, but I have found a tricky way to do it. Thanks

I'm glad you found a workaround :-) Still, it's odd that MainStage doesn't see those sounds in their usual (factory) location.. Maybe it needs to refresh the patch list—unfortunately there doesn't seem to be an easily accessible command for that in MS like the Refresh command for the EXS instrument list in Logic..