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

2133 $\rightarrow$ 9 $\left(X\right) $

2343 $\rightarrow$ 12 $\left(/\right)$

3474 $\rightarrow$ 18 $\left(X\right) $

4131 $\rightarrow$ 9 $\left(X\right) $

5286 $\rightarrow$ 21 $\left(/\right)$

5340 $\rightarrow$ 12 $\left(/\right)$

6336 $\rightarrow$ 18 $\left(X\right) $

7347 $\rightarrow$ 21 $\left(/\right)$

8115 $\rightarrow$ 15$\left(/\right)$

9276 $\rightarrow$ 24 $\left(/\right)$

Required number of numbers = 6.