Alex, (hoping you are able to read in German or have someone along to translate accordingly) 

http://www.aerzteblatt.de/archiv/48792; 

http://die-prostata.com/weibliche-prostata-g-punkt/; 

http://hebammenhandwerk.de/Weibl_Genitaldrusen_Eine_sprudelnde_Quelle_der_Lust_DHZ_10_2007.pdf; 

G-spot = " G-Punkt  /  Gräfenberg "  just to encourage you to perform an e. g. Google search (also in German...   e.g.  

| G-Punkt AND GRÄFENBERG AND WEIBLICHE PROSTATA AND Anatomie AND HISTOLOGIE | ,

you also could perform such a search in English... e.g.:

| G-point, AND/OR G-spot, Gafenburg AND OR GRÄFENBURG AND FEMALE Prostate AND ANATOMY and HISTOLOGY AND NERV* |

Sources in ResGate:  https://www.researchgate.net/post/Are_vaginal_orgasm_and_G-spot_a_scientific_fraud?;

https://www.researchgate.net/search.Search.html?type=publication&query=Gr%C3%A4fenberg ; 

naturally also: 

https://www.researchgate.net/search.Search.html?type=publication&query=GRAFENBERG

(only as examples…PubMed at

i) http://www.ncbi.nlm.nih.gov/gquery/?term=Gr%C3%A4fenberg  and specially then ii)  at: http://www.ncbi.nlm.nih.gov/pmc/?term=Gr%C3%A4fenberg  or iii) at http://www.ncbi.nlm.nih.gov/pubmed/?term=Gr%C3%A4fenberg  or iv) at  http://www.ncbi.nlm.nih.gov/nlmcatalog/?term=Gr%C3%A4fenberg

Good luck!

Check this article

http://onlinelibrary.wiley.com/doi/10.1002/ca.22523/full