To be divisible by 3, the sum of the digits must also be divisible by 3. There are 7 ways to select 6 digits out of 7:
012568 012569 012589 012689 015689 023689 125689. If we now sum the digits we get respectively:
22 23 25 26 29 28 31. None are divisible by 3. So there are no 6-digit numbers divisible by 3 using 6 out of the 7 given digits.