I have the 2016 street bob with the combination led lights. I need to get some more 4 core cable to suit, i cant seem to find any locally,  anybody know somewhere that would suit?

Get some 5 core trailer wire from any auto lecky or supacheap. Use 4 and have a spare!

just use speaker cable x 2
when I did mine, I cut the connector off & ran the existing cable through the hollow bolts, extended with speaker wire and soldered the original plug to the end of the speaker wire & all ok, mine was only 2 core but you may find 4 core guitar pickup wire will do the job as well