ANY Realtor can be "approved" by NACA. The Realtor simply agrees to pay NACA one third of the commission they ultimately earn when you buy a house. If you already have a Realtor, he/she can go to the website to get the referral agreement forms and submit to be "approved".
If you haven't already signed up online with NACA, it would be best for your Realtor to sign you up so she/he will not have to pay the large "fee" to NACA.
All the best,