Dear Ms. Sabine Tauscher,

I can imagine your problem.... but don't know whether you use whole isolated / or whole isolated, fixed, dehydrated and paraffin embedded  / or frozen sections of murine pancreatic islets of Langerhans for mounting on glass (what is the basic purpose using these?), since

usually "Superfrost" slides (treated either physically or also chemically)are used for better adhesion or better attachment tissue sections -frozen or paraffin embedded) and have been reported to be of help regarding adhesion problems. In your case, using glass cover slips/slides I am not aware there such special "coated" glass is on the market or sold. So (if my knowledge is right....I haven't searched yet for a commercial source) you only can rely on your practical skills in preparing your glass coverslips by yourself....APES, Polylysine, or (classically) Chrome alum - gelatine (old but quite sticky...).   In eventu: Search Google for: | adhesi* cover glass slides APES Polylysine |  or for reduced number of specific results: |  adhesi* cover glass slides APES Polylysine chrom alum-gelatine chrome alum |

Also, eventually cf: 

https://www.fishersci.com/us/en/products/I9C8JXLT/adhesion-microscope-slides.html ; or https://www.emsdiasum.com/microscopy/products/histology/slides.aspx 

Disclaimer: no affiliation to companies mentioned, no financial interest.

Frohe Ostern!