The Gene Expression Atlas does have expression data by at least tissue type. It also includes the tissue data from the Human Protein Atlas. It's not that intuitive to navigate but if on the home page you select for example human as species and pancreas as biological condition, the search result is a list of experiments several of which have looked at multiple human tissues like those of the GTEx project. Clicking on one will show you a table of genes x tissues with the corresponding expression levels. For example selecting the GTEx data set, you can see that INS (insulin) is only expressed in the pancreas. If you want data by precisely defined cell types, you can have a look at the HPA tissue atlas, they have immunostaining data for cell types within tissues, e.g. check the left hand side of this page for pancreatic cell types.