You can search the following to see if they have the data you need:

• You may want to try searching Hugging-Face for some datasets that you can read in and perhaps extract the list of diseases you're looking to populate. There's a promising dataset on hugging-face here, where you could create a set of all dieseases: https://huggingface.co/datasets/QuyenAnhDE/Diseases_Symptoms
• You may want to try searching Kaggle for some datasets; for example, you could extract the public domain data from the "medical conditions" column from the dataset here: https://www.kaggle.com/datasets/jithinanievarghese/drugs-side-effects-and-medical-condition ... or extract disease text from a simpler dataset here: https://www.kaggle.com/datasets/niyarrbarman/symptom2disease

You should search Pypi for projects similar to your own. I don't use any medical python libraries, but there are perhaps python libraries out there that access similar datasets that you are looking for, like https://pypi.org/project/pyhealth/ (You can go to their project page, they list their datasets)