Here:
https://functionaldata.wordpress.ncsu.edu/resources/
Also, look here to know about the packages which contain said datasets:
https://cran.r-project.org/web/views/FunctionalData.html
As a general rule, when you look for new packages in R, start from the CRAN Task Views. Another good place to look for datasets is
However, as all sites in the SE hierarchy, asking questions on Open Data is a bit more complicated than here. Fairly strict rules about on-topic/off-topic questions, and about what constitutes a good question, are enforced: this helps keeping the quality of the Q&A high, but it makes for a steeper learning curve.
Scalar-on-function regression, and generally FDA (Functional Data Analysis) is not a very trendy topic today: there are relatively less research groups working on it, than on other topics. Not that there's anything wrong with it! But just out of curiosity, since it's not common today to find people familiar with scalar-on-function regression, may I ask why you're studying it?