You may use Stack Overflow to ask/answer specific PHPUnit problems.
You may get real-time support or advice for PHPUnit on Gitter or IRC chat.
If you need support with PHPUnit, for instance with introducing it into your organization to improve your PHP development process, then thePHP.cc can help you.
thePHP.cc is the consulting company for PHP and related technologies co-founded by Sebastian Bergmann, the creator of PHPUnit.