You can use RefEx, MGI. Here are the links :

RefEx :

https://refex.dbcls.jp/index.php?lang=en&db=mouse

MGI :

http://www.informatics.jax.org/expression.shtml

BioGPS :

http://amp.pharm.mssm.edu/Harmonizome/dataset/BioGPS+Mouse+Cell+Type+and+Tissue+Gene+Expression+Profiles

I didn't use it myself. But this one seems to be good:

https://tabula-muris-senis.ds.czbiohub.org/

It is a single-cell transcriptomic atlas that includes data from 23 tissues and organs across the lifespan of the Mus Musculus.

Here is the link to the paper: https://www.nature.com/articles/s41586-020-2496-1