To join the CNYIRA, you need to pay the fee ($30 for individual, $35 for family membership) and fill out the form (see the link below for the form.) Or, show up at one of the races. The registrar at the event will have the forms. However, if you want to reserve a car number ahead of time, you need to join ahead of time. Funny how that works.
The other form below is the event entry (registration) form. Print that and fill it out, and bring it with you to the event to speed up registration.