Marking (/) those which are are divisible by 3 by not by 9 and the others by (X), by taking the sum of digits, we get:s

2133  9 (X)

2343  12 (/)

3474  18 (X)

4131  9 (X)

5286  21 (/)

5340  12 (/)

6336  18 (X)

7347  21 (/)

8115  15 (/)

9276  24 (/)

Required number of numbers = 6.