Data are publicly available for the GREGOR instruments GRIS, GFPI, and BIC/HiFI. The BBI and ZIMPOL do not yet have a public archive.
If you use GREGOR data, please include the following acknowledgment in your publication:
The 1.5-meter GREGOR solar telescope was built by a German consortium under the leadership of the Leibniz-Institute for Solar Physics (KIS) in Freiburg with the Leibniz Institute for Astrophysics Potsdam, the Institute for Astrophysics Göttingen, and the Max Planck Institute for Solar System Research in Göttingen as partners, and with contributions by the Instituto de Astrofísica de Canarias and the Astronomical Institute of the Academy of Sciences of the Czech Republic.
Please cite also the respective instrument papers from the special issue of Astronomische Nachrichten (Vol. 333/9), especially Schmidt et al.2012, AN 333/9, 796 and Kleint et al. 2020, A&A, 641, A27 (https://arxiv.org/abs/2006.11875).