He wanted pro-amalgamation groups to condemn the vandalism and advise their supporters to avoid such acts.
Damon Harvey, a spokesman for pro-amalgamation advocacy group A Better Hawke's Bay Trust, said the trust did not condone the attacks, support or have any involvement in such activities.
Mr Nash said he accepted neither the trust, nor the National Party, were involved.
"But it's someone who obviously believes the stance of A Better Hawke's Bay," he said.
"This is a very deliberate, calculated act. They would have to go to quite a bit of time and effort and also money to get this done. That's why I've gone to the police."
He repeated an offer he made last month of a $500 reward for information leading to charges.
"The irony is these attacks just give more oxygen to the amalgamation issue ..."
Police had told him they would try to check CCTV cameras for suspicious activity.