For quick, up-to-date, at-a-glance stats on gun violence, check the RAND, Gun Violence in America Report, GVA, or Mass Shooter Database. To drill down the datasets, check the sources from ATF, BJS, CDC or FBI.
For more sources on polls and public opinion data, click here.
Search the survey or polling agency websites using gun as a keyword. For example, GSS has about 20 variables related to guns over the years including public opinion questions (favor/oppose restrictions), gun ownership, and even if respondents have ever been threatened with a gun.