SOP are not made for department. SOP are usefull to perform a task.
as there are various tasks which comes under HR department, differet SOPs need to be made for different tasks.
You can hire some consultant to do the same, but better if you try to make it yourself. As SOP is a checklist of activities to be performed to complete a task, an executer can better decide the SOPs
Regards
Daleep Sharma