Visit several real estate offices to find the agent who provides the service you deserve. as you said your looking for someone to represent you,Then you hire a buyers agent hired to work in your best interest to make sure you get what you want. the profesional you hired should be familiar with the financial requirements with each cooperative building and transactions, also explain that you need to get approval by the board before the purchase of a cooperative.
Just in case you haven't been pre-approved yet, However, An agent that knows the process would guide you threw it. Good Luck.