Personally I’ve been lucky enough to find it via word of mouth/recommendation and also directly approaching clients. Most contractors get their work through recruiters though, if you mention to a recruiter you are interested in contract work you’ll start getting a ton of phone calls and emails. It’s not uncommon for contracts to get extended several times, and you’ll probably build up a network of other contractors quite quickly.

One thing you might find is getting your first contract is hard if you are in a permanent job - companies generally are looking for contractors to start ASAP, so a one month notice period (with the risk that you get tempted to stay at your existing company) is often not acceptable to them. Some clients will wait for the right person but you might find you need to quit your job first before finding work which can be a bit nerve wracking - so it’s wise to survey the market, talk to recruiters etc. for a while before doing so!

If you’re UK based https://github.com/tadast/switching-to-contracting-uk/blob/m... may be interesting.