I suggest a search of the (U.S.) National Library of Medicine's PubMed database using "mouse eeg.". Attached is online access to the results of this type of search. Also attached is one citation ("Pharmaco-EEG Studies in Animals: A History-Based Introduction to Contemporary Translational Applications") that you will find in PubMed,..

https://www.ncbi.nlm.nih.gov/pubmed/?term=Mouse+eeg

https://www.ncbi.nlm.nih.gov/pubmed/26901675

Rodrigo Quian Quiroga, from University of Leicester, England, hosts a small database of EEG and EP recording data, both human and animal in his page at Caltech. Included is a small set of short (5 sec) EEG recordings from rats (original source: Giles van Luijtelaar and Joyce Welting). Also he points to the papers where these datasets originated. I don't know if these fit your needs. Maybe he can provide access to larger sets too. Here: https://vis.caltech.edu/~rodri/data.htm

Additionally you might find some use of the research from this team from University of Science and Technology, Korea: https://www.jove.com/video/2562/high-density-eeg-recordings-freely-moving-mice-using-polyimide-based (Lee, M., Kim, D., Shin, H. S., Sung, H. G., & Choi, J. H. (2011). High-density EEG recordings of the freely moving mice using polyimide-based microelectrode. JoVE (Journal of Visualized Experiments), (47), e2562-e2562.)

They may be willing to share their data.

https://vis.caltech.edu/~rodri/data.htm

https://www.jove.com/video/2562/high-density-eeg-recordings-freely-moving-mice-using-polyimide-based

I think the following resource is more affluent: http://www.opensourceinstruments.com/SCT/Recordings/index.html

Among the sets provided are 4 hours recordings of two mice (Mouse Classifier_Example) in the .ndf format. They are playable with the Neuroarchiver, part of the LWDAQ suite of tools, all distributed for free by the Open Source Instruments, Inc. under the GNU General Public License.

http://www.opensourceinstruments.com/SCT/Recordings/index.html

http://alignment.hep.brandeis.edu/Software/

http://www.opensourceinstruments.com

3-CHANNEL EEG/EMG TETHERED MOUSE SYSTEM

Pinnacle’s THREE-CHANNEL TETHERED MOUSE SYSTEM allows researchers to simultaneously record three channels of EEG and/or EMG data. The data conditioning and acquisition system (DCAS) and preamplifier are preconfigured and ordered as a matching pair. Fully independent preamplifiers are also available.

SYSTEM BREAKDOWN

http://www.pinnaclet.com/3-channel-eeg-emg-systems-mice.html