There is a program called PhotochemCAD (see https://onlinelibrary.wiley.com/doi/10.1111/php.12860) which contains a database of experimental absorption and emission spectra of more than 300 organic and organometallic compounds. The spectra are available in plain text form. While the maximum absorption wavelengths of the most intense peaks of each compound have already been tabulated in the main text of the linked article, if you are also interested in the absorption maxima of weaker peaks too, you may need to extract this information from the spectra by yourself.

By the way, given that the database contains complete spectra information, it may actually be a good idea to train your model to reproduce the overall line shape instead of just the absorption maxima, giving an even more useful model :)

There is a program called PhotochemCAD by Tanuchi and Lindsey which contains a database of experimental absorption and emission spectra of more than 300 organic and organometallic compounds. The spectra are available in plain text form. While the maximum absorption wavelengths of the most intense peaks of each compound have already been tabulated in the main text of the linked article, if you are also interested in the absorption maxima of weaker peaks too, you may need to extract this information from the spectra by yourself.

By the way, given that the database contains complete spectra information, it may actually be a good idea to train your model to reproduce the overall line shape instead of just the absorption maxima, giving an even more useful model :)

Taniguchi, M.; Lindsey J. S. Database of Absorption and Fluorescence Spectra of >300 Common Compounds for use in PhotochemCAD in Photochem. Photobiol. 2018, 94, 90-327; doi 10.1111/php.12860.

Project page: https://www.photochemcad.com/