RESP files can be downloaded from IRISDMC or generated from a dataless SEED using software tools.
With a dataless SEED file, rdseed can generate a RESP file. PDCC can also write the contents of a dataless SEED for a selected station in RESP format.
IRIS DMC keeps a RESP FTP file repository for all stations it archives. You can easily get to this repository at http://www.iris.edu/pub/RESPONSES. IRIS DMC also maintains factory-spec representations of instruments in the form of RESP files in its Nominal Response Library ( http://www.iris.edu/NRL ).