Don't believe there's a relay. They're inherently built into every E90. The difference in the US, is that the switch doesn't include the button to activate them.
This gentleman from Texas, I had found posting on the other E90 site (e90post), where I got in touch with him and he sold me a DIY modified switch that activates the rear fogs for a much lower price than what you would buy from Overseas, ECSTuning, or the like. https://www.facebook.com/MyBMWLEDs/?fref=ts
Give him a message. He took care of me just great, and I'm sure he'll do the same for you.
I think the cars sold in South Africa already have the rear foglights enabled. So pehaps the OP has a problem with them not functioning.
I believe the rear foglights do not have a relay; they are activated by the footwell module.
From the E90 Bentley Service Manual: "Footwell module (FRM) is the master control module for all exterior lighting functions. Exterior light systems (headlights and side and parking lights) are switched ON and OFF by the light switch via the FRM....."
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