OpenAI Presence is available to eligible enterprise customers as a deployed product through a limited general availability program. Deployments are led by OpenAI Forward Deployed Engineers and select global systems integrators. Presence is not yet available as a self-serve product.
Building your own enterprise chatbot with in-house domain experts is the only path that makes sense to me. The software piece is really not that difficult. There are a lot of examples and options to pull from now. You could maybe implement a custom MCP server and use the M365 copilot on top if you don't want to reinvent the wheel.
I think bringing in OAI consultants is probably a mistake in most cases. I've already seen one AI consulting team and they just cannot get deep enough fast enough. It would take them years of suffering our codebase and daily procedures to get to the point where they could actually make an impact.