Atlassian provides non-profit or community licnenses of add-ons sold on the Marketplace. However vendors cannot generate these licenses.
Organizations eligible for non-profit or community licenses of Jira must contact Atlassian. See below for a quote from Atlassian's web site.
Atlassian supports organizations that seek to do good in the world. Charitable organizations can apply for no-cost Community licenses. Once a customer has a Community license for any Atlassian product, they can request additional licenses from Atlassian sales representatives, including Community licenses for add-ons they obtain through the Marketplace.
Your customers can apply for an Atlassian Community license here:
http://www.atlassian.com/software/views/community-license-request
Customers with an existing Community license for any Atlassian product, should request a Community license for your add-on by emailing sales@atlassian.com.