Welcome to the forum. Several people have voiced the same concerns (see for example Where is my Experimental 0827? Can you announce it before? It's shocked me! and Will the experimental models return? ) and it would certainly be useful to have the experimental models reinstated in AI Studio.
In any case, the experimental models are available from the API. The list_models operation currently returns these experimental models:
models/gemini-1.5-pro-exp-0801
models/gemini-1.5-pro-exp-0827
models/gemini-1.5-flash-exp-0827
models/gemini-1.5-flash-8b-exp-0827
models/gemini-1.5-flash-8b-exp-0924
Hope that helps.