You can find these by opening game executable with a hex editor.
These can be used in the <field name="Key"></field> tags scattered around the *.dbx settings files
IDK_Undefined IDK_Pause IDK_MediaSelect IDK_Mail IDK_MyComputer IDK_WebBack IDK_WebForward IDK_WebStop IDK_WebRefresh IDK_WebFavorites IDK_WebSearch IDK_Wake IDK_Sleep IDK_Power IDK_AppMenu IDK_RightWin IDK_LeftWin IDK_Delete IDK_Insert IDK_PageDown IDK_ArrowDown IDK_End IDK_ArrowRight IDK_ArrowLeft IDK_PageUp IDK_ArrowUp IDK_Home IDK_RightAlt IDK_PrintScreen IDK_Divide IDK_NumpadComma IDK_WebHome IDK_VolumeUp IDK_VolumeDown IDK_MediaStop IDK_PlayPause IDK_Calculator IDK_Mute IDK_RightCtrl IDK_NumpadEnter IDK_NextTrack IDK_Unlabeled IDK_Ax IDK_Stop IDK_Kanji IDK_Underline IDK_Colon IDK_At IDK_PrevTrack IDK_NumpadEquals IDK_Yen IDK_NoConvert IDK_Convert IDK_Kana IDK_F15 IDK_F14 IDK_F13 IDK_F12 IDK_F11 IDK_OEM_102 IDK_Decimal IDK_Numpad0 IDK_Numpad3 IDK_Numpad2 IDK_Numpad1 IDK_Add IDK_Numpad6 IDK_Numpad5 IDK_Numpad4 IDK_Subtract IDK_Numpad9 IDK_Numpad8 IDK_Numpad7 IDK_ScrollLock IDK_Numlock IDK_F10 IDK_F9 IDK_F8 IDK_F7 IDK_F6 IDK_F5 IDK_F4 IDK_F3 IDK_F2 IDK_F1 IDK_Capital IDK_Space IDK_LeftAlt IDK_Multiply IDK_RightShift IDK_Slash IDK_Period IDK_Comma IDK_M IDK_N IDK_B IDK_V IDK_C IDK_X IDK_Z IDK_Backslash IDK_LeftShift IDK_Grave IDK_Apostrophe IDK_Semicolon IDK_L IDK_K IDK_J IDK_H IDK_G IDK_F IDK_D IDK_S IDK_A IDK_LeftCtrl IDK_Enter IDK_RightBracket IDK_LeftBracket IDK_P IDK_O IDK_I IDK_U IDK_Y IDK_T IDK_R IDK_E IDK_W IDK_Q IDK_Tab IDK_Backspace IDK_Equals IDK_Minus IDK_0 IDK_9 IDK_8 IDK_7 IDK_6 IDK_5 IDK_4 IDK_3 IDK_2 IDK_1 IDK_Escape IDK_None
IDP_POV_Undefined IDP_POV_2 IDP_POV_1 IDP_POV_0
IDB_Button_Undefined IDB_Button_7 IDB_Button_6 IDB_Button_5 IDB_Button_4 IDB_Button_3 IDB_Button_2 <----- Middle Mouse Button IDB_Button_1 <----- Right Mouse Button IDB_Button_0 <----- Left Mouse Button
IDB_Undefined IDB_Rtrigger2 <----- R1/RB (button 5) IDB_Ltrigger2 <----- L1/LB (button 6) IDB_Rtrigger <----- START (button 8) IDB_Ltrigger <----- SELECT/BACK (button 7) IDB_alt <----- Left stick press (button 9) IDB_start <----- Right stick press (button 10) IDB_Rthumb <----- button 12 IDB_Lthumb <----- button 11 IDB_Rtopright IDB_Rtopleft IDB_Rright <----- □/X (button 3) IDB_Rleft <----- ✕/A (button 1) IDB_Rdown <----- ◯/B (button 2) IDB_Rup <----- △/Y (button 4) IDB_Lright IDB_Lleft IDB_Ldown IDB_Lup
IDA_Undefined IDA_Axis7Y IDA_Axis7X IDA_Axis6Y IDA_Axis6X IDA_Axis5Y IDA_Axis5X IDA_Axis4Y IDA_Axis4X IDA_Axis3Y IDA_Axis3X IDA_Axis2Y IDA_Axis1YNeg IDA_Axis1XNeg IDA_Axis1YPos IDA_Axis1XPos IDA_Axis1Y IDA_Axis1X IDA_Axis0YNeg IDA_Axis0XNeg IDA_Axis0YPos IDA_Axis0XPos IDA_Axis0YThese, plus IDA_Axis2X (mouse wheel) and IDA_Axis0X, which are in another position in the exe.
IDA_Axis0X/IDA_Axis0Y is the controller left stick when in PadInputActionData GUIDs. Mouse when in MouseInputActionData ones
EDIT(final): Ok, to sum up.. this game only reads buttons from 1 to 12 and X/Y/Z Axis + Z Rotation.
Nothing else, not even DPAD/POV. After many attempts with SCP vJoy DirectInput device there weren't others accepted.
Other people seem to just have had problems with deadzones..
and solved everything by tinkering with config files, but imo, that must not be the whole story.
At the moment, the best way to play the game with a controller seems some combinations of XInput Plus and conventional remapping softwares like antimicro