Richard,
The local club does not organize judging in an MCA event, which is why you did not see that on any forms. The "normal" process as I understand it is to (1) join MCA, (2) take and pass the online test for certification, (3) contact the appropriate (for the year and class) assistant national head judge (ANHJ) and let them know what show(s) you will be attending and discuss what you would like to do. Names and contact info is on the MCA website, (4) show up and meet with the ANHJ, get assigned to a team, and go to work.
The alternative process would be to just show up and talk to the ANHJ to see if there is an opportunity for you to join a team. If allowed the intent would be to whet your appetite enough to join, take the test, and become certified. The risk here is that there are more than enough certified judges to load up each team, and a "walk ins" doesn't get placed. There was one event for me where there were so many 67-68 concours judges that some were volunteered to venture into the daily driven class which needed a lot more judges.
My experience.
I highly recommend that you take the online test - you can do it!