Need reliable source for 30+ years of S&P 500 historical data for LSTM/Transformer research [P]

Hi everyone, I'm starting a research project on financial time-series forecasting using LSTM and Transformer models for predicting S&P 500 market direction. Right now, I'm struggling with obtaining reliable long-term historical data. I tried Yahoo Finance, but downloads are inconsistent/failing for me, and most Kaggle datasets I found only contain around 5-10 years of data.