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Lie detector tests are not very commonly used (most courts disregard their weight, especially in CA) as the results can be easily manipulated as well as presenting unreliable false positives due to stress of the test taker.
So if you are pursing one in the hopes that you can introduce the results in a court proceeding, you may want to save your money.
But if you want one for some other reason, there are plenty of people out there that run them (with varying levels of credibility). HR staffing firms for executive and security positions will be able to give you referrals (you can contact them and ask who they use), you can also contact the local bar association (they may be able to give you a referral, although as I noted, this is not commonly used in court proceedings).
Be careful with who you select, there are many charlatans out there, so once you actually get a referral, ask for (and actually check with) references, as well as the BBB or other third party resources.