In my experience the ignition live is always needed to operate the head unit, therefore you will need to 'splice' in to an ignition 12v live to get the head unit to work conventionally as when you turn the ignition 'OFF' the head unit will know to 'power off'.
Unconventionally you can 'double up' the ignition live cable on to a permanent 12v live - this would allow the head unit to operate whenever you turn it on - even with the keys out of the ignition! This is not
a good way to do it as you could accidentally leave the head unit 'On' and flatten the battery - bad times!!
Finding a 12v ignition live should not be too hard as long as you have a means of testing for power eg a Multimeter. The 'splices' you can get from Halfords / Cafco etc; check out eBay item no. 290584374250
The splice is 'crimped' using a pair of pliers!
Hope this helps! Regards MV