I was at Myrtle Beach the last weekend in May. I can confirm that Myrtle Beach Police and Fire Departments, and North Myrtle Police and Fire Departments are all on the Horry County system.
I think the best to listen to is Myrtle Beach PD on the waterfront, Myrtle Beach FD, and Horry County Fire and Rescue (County Fire and EMS together[mostly Disptach, TAC1 and TAC2]). That should keep you busy!!
Q