Set up an account on MailChimp - it's free until you hit 500 subscribers. Embed the email signup form on the company website. Also, at store checkout ask if they want to sign up to the email list and hand them a tablet and capture their name/email/group preference right there.
MailChimp has an option to have one list with different groups so that if someone signs up to the list and they want to know when blueberry season is, they can sign up for the blueberry group.
MailChimp allows for people to sign up for more than one group, within one list. Salespeople can login to the mailchimp account and see who is in what group and then contact them when that particular plant/tool/high end equipment comes in.