Hi Aimee Neary,
Greetings and Welcome to Microsoft Q&A forum!
At the moment, fine-tuning for the GPT-4o model is available in the East US2, North Central US, and Sweden Central regions. For GPT-4o mini, fine-tuning is supported in the North Central US and Sweden Central regions. You can find more details on model availability here: Fine-tuning model regions.
However, there hasn't been a specific timeline announced for when fine-tuning will be available in the East US region for GPT-4o model finetuning and EastUS and EastUS2 regions for GPT-4omini model finetuning. I understand the constraints your organization faces, and I recommend you to use GPT-4o model which is available in EastT US2 region for finetuning and keeping an eye on the Azure OpenAI Service updates for any future announcements Azure OpenAI Service Updates.
Let me know if this solves your issue and if you have any other questions. Thank you!