Architect doesn't have time to finish my construction drawings.

I hired an architect who works fulltime for a University and moonlights creating house plans.

about three months ago he said he did not have time to continue working on the plans. He has two young kids, a wife, and a fulltime job. I totally understand where he is coming from. We agreed he'd finish the plans and we'd be done. The plans are for a prefab home that I plan to build and sell. The state (L&I) requires mechanical and electrical drawings and he has not included them in the construction drawings. I have reached out to him and asked how to proceed and have not heard back. Can additions be made to the plans by another architect or does the original architect need to make the additions? What if he decides he doesn't/can't work on them anymore? Where do I go from here? I have paid him so it's not a money issue. He gave me an amazing discount for it taking too long. There is nothing negative between us. I believe he is honestly too busy and is wanting to spend his evenings with his family not work after he's already worked all day. I'm at a loss as to how to get this project finished with out him. Thank you for any advice offered