Although there are no groups that explicitly support pansexuality alone, there are many who specifically include resources, information, interviews, and projects dealing with pansexuality.
In the United States, the Bisexual Resource Center states that they support bi+ people, explaining that this means pansexual, fluid, omnisexual, queer, and all other free-identifiers. BiNET USA is one of the most commonly known support organizations for bisexual, pansexual, fluid, queer, etc. groups, as well as one of the oldest in the country. GLAAD specifically works on acceptance and advocacy within media for LGBTQIA+ groups, and they specifically mention pansexuality in their mission statement and in their ongoing work.
Internationally, Human Rights Watch supports and advocates for all LGBTQIA+ groups, including pansexuals, which it groups with bisexual and polysexual orientations in their project areas description. The International Lesbian, Gay, Bisexual, Trans and Intersex Association (ILGA) also works for all LGBTQIA+ groups within countries around the world, supporting local efforts to advocate for rights and support individuals. They provide information about pansexuality and include regular discussions and interviews from pansexuals in their resources.