Plug top fuses are commonly available in 3,5 & 13A.
You can also (easily) get 1,2,7 & 10A though. Not sure about 4/6/8/9/11/etc tho!
What power, in watts, does your PA potentially draw? Look on back/side/or the manual of the unit. If you can find the wattage then take your power (eg)...