A few years ago I found out my great-grandfather was of slovene ethnicity and that his family used to live in one of the slovene neighborhoods near Gorizia, which today is part of Italy.
I had an opportunity to visit the city of Gorizia for a few days, during which I sought books regarding the 19th century slovene community, with no success.
I was told by an italian-slovene that it would be difficult to find books in Italian regarding this theme due to a historical animosity between the Italians and Slovenes that has existed since they had to fight each other in the world wars.
Nevertheless, if you have any recommendation about books that consider this scope, would you share it with me?
Interesting! So I'm an Italian from the region, though I've had my doubts sometimes. Italians can tell I'm Italian but based on my name they can immediately point out that I'm either Venetian or from the Friuli and yet no one else has ever guessed that I was Italian, they always guess German or Polish.
Finding writings about this region or even Dalmatia pre-19th century is very easy (especially if you can read in Italian), but the 19th century your Italian-Slovene friend is kinda right.
IF you can read Italian a primary source would be Graziadio Isaia Ascoli; a Jewish man born in Gorizia in the 19th century. He was an Italian linguist and I do believe you can look up his archive by just searching it on a search engine. Other than that there is a link to a journal I can send you, it's in English if you want to PM me.
The reason I said the gentleman was kinda right is because most of the animosity arose after WWI where the fascists tried to force Italianize not only the non-Italians such as the Slovenes, but even the Italians themselves. To this day dialects vary in Italy, I can go to Lombardy and can already tell the difference in how they speak despite the fact that they are speaking "Northern" Italian. The Italian national language pushed during Fascism was the Florentine kind which was already being pushed in the 1800s. Ascoli had an approach of sort of 'combining' the different dialects rather than forcing one. Nonetheless, according to my great-grandfather whom I never met -as a matter of fact, I never even met my grandpa; in any case, according to my great-grandfather he remembers Slovenians assisting Italians in their struggle against the Austrian Empire. And according to both my great-grandpa and my grandpa, they remember the poor treatment of Slovenians getting politically assaulted or being called socialists because the country of Slovenia was part of Yugoslavia. So my father told me that his grandfather (my great-grandfather), remembers his Slovenian neighbors leaving to go to Argentina. Many probably came to the USA and many probably crossed the border to Yugoslavia. This last bit is word of mouth from my family member, so take it for what it's worth.
If you don't speak/read Italian and ever find a passage you need me to translate just PM me, I don't mind. And if for some reason you want to go a bit further back on the subject you can check these 2 books out(if you can read Italian that is):
Bibliografia del Friuli by Giuseppe Valentinelli
Historia della principale contea di Goritia nella provincia Foro-Juliense by Giovanni Giacomo d'Ischia