Agree with the statement in post #3 above that LACs can feel small & that everyone knows everyone else’s business. This may not be a great environment for a shy, introvert.
Post #8 also offers some cautionary advice to consider.
Small, rural LACs can be a cruel environment for a student who doesn’t fit in.
I can see Vassar, Skidmore, and Wesleyan as being more accepting as well as Haverford College–assuming that your son feels comfortable in a liberal environment.
I do not think that any of the schools discussed can be considered as a nurturing environment where social skills can be developed. Your son will either develop such skills or risk being alone with just a friend or two. No school will babysit your son.
Consider Grinnell College in Iowa. Grinnell kids are kind & social & sensitive to differences as the school has a significant (about 20%) number of international students.
Broadly speaking, schools with a sizeable number of international students may be a great environment for a very shy introvert as he will not be judged or categorized quickly as might occur in a more traditional environment. International students tend to be more cautious & more considerate & more accepting of differences.