There is no legacy simvar for those buttons because they never had any functionality until FS2020 SU10. You can only toggle them on and off with B or H events. 2024 will not work because _TOGGLE does not work for B events though SImConnect yet. See - EnumerateInputEvents doesn't return _INC, _DEC, _TOGGLE, _ON, and _OFF events
FS2024
B:AS1000_Play_MidCom_Toggle
B:AS1000_AUX_MidCom_Toggle
B:AS1000_MAN_SQ_MidCom_Toggle
B:AS1000_COM_Tel_MidCom_Toggle
FS2020
H:AS1000_MID_AUX_Push
H:AS1000_MID_MAN_SQ_Push
H:AS1000_MID_Play_Push
TEL is unclickable