I don't think there is any way to get certified except for at the scheduled dates and locations. These also fill up quickly, so it is a good idea to plan ahead.
Calendar of Events - Testing Dates
Those administering the test are doing so voluntarily and without pay - indeed they are paying their own way to get to the facilities and for accomodations while there.
The workshop is given at those locations prior to the actual testing. It is also a good idea - after you feel you are ready for the test - to try to find an MCI (if possible) or an experienced CCI to run you through the test informally well before the actual test so that he can see your weaknesses and strengths and advise you on how to further prepare for the test.
Jackster or others may have more information for you. The casting and written portions of the test - though they must be done well - are not the main part. It is your understanding of casting mechanics and how to convey them to a student in different ways that is the main thrust of the test.