There isn't a set rule. You either go through your network, e.g. former colleagues, friends of friends or clients or other consultants from previous projects.
That being said, I am in a position now where I can take on extra work and provide more consultancy services, so will be looking to ramp up my outreach.
I have had to fix quite a lot of mess here in the UAE/GCC where cheaper, outsourced labour was let loose on clients' projects.