This is the website on which I bought the Valentinian I gold solidus: https://www.aucm.com/inventory.html?product_list_order=price_desc Maybe there is something which interests you on it.
The Diocletian gold aureus you like was also unsold in the previous auction it was in last year: https://www.numisbids.com/n.php?p=lot&sid=7487&lot=214
Its unique. It was smoothed/ probably reason it was not sold. Still a RARE coin. I have FDC one from Triton V CNG. Otherwise I might have bought that one.
This one of Carinus that was minted in Siscia sold for 30000 CHF a little less than 2 weeks ago: https://www.numisbids.com/n.php?p=lot&sid=7904&lot=2386
In Croatia of course!: https://en.wikipedia.org/wiki/Salona The modern town is called Solin: https://en.wikipedia.org/wiki/Solin
Gold coins from the Salona (Salona is Diocletian's hometown by the way) mint do exist, but it would seem only in museums, I have never seen one on the market.
I just bought this Empire of the Romans Bronze 1/2 Follis of Justinian I (minted in Salona sometime between 550 and 553):
My maximum bid (4000 EUR) on the Diocletian Aureus has already been reached! I think the chances of me winning it now are only minimal...
Sirmium was also a Croatian city at various points in history, firstly in the early 9th century, when it was a part of the Duchy of Lower Pannonia, which at that time was led by Ljudevit Posavski, and most recently during World War II (when it was called Hrvatska/Croatian Mitrovica), at the end of which the communist monster Tito gave it to the Serbs.
My bid for the Diocletian Aureus was withdrawn at my request, because after I had made the bid I took a closer look at the coin and saw that something was wrong in the area to the left of the lips, and since no defects whatsoever were mentioned in the description, I asked them about it and they re-examined the coin and concluded that it was a flan flaw, after which I sent them a request to withdraw my bid, and it was granted this morning.
An aureus of Diocletian from the Antioch mint will be on offer at the next Rauch auction: https://www.numisbids.com/n.php?p=lot&sid=8129&lot=384 I won't bid on it.
Apart from the 3 Emperors of the original/united Roman Empire who were born in Croatia, there was at least one more Roman Emperor who was born in Croatia, the last recognized Emperor of the Western Roman Empire Julius Nepos: https://en.wikipedia.org/wiki/Julius_Nepos I have put in a bid for a tremissis of his: https://www.numisbids.com/n.php?p=lot&sid=8081&lot=1148
Medieval Croatia (Ragusa): silver grosso portraying St. Blasius and Christ, ca. 1372-1438 Obverse: S BLASIVS RAGVSII, Saint Blasius standing, facing, raising hands in benediction and holding crozier. Reverse: IC/XC, Christ standing facing, raising hand in benediction and holding Gospels. Ex-Künker am Dom, Munich, Germany, 5/9/2015. I used to call this my "Hippie Coin". Saint Blasius looks a little bit like Tommy Chong there, doesn't he? (And Jesus looks rather annoyed.)
This is up for auction today: https://www.sarc.auction/SLAVONIA-H...0-1270-AR-denar-0-79g-ND-ca-1267-69_i52801854
I know nothing about the Gepids, but that’s a sharp siliqua. The lettering is much clearer than I’d expect on a Germanic coin of the era. It looks almost as well executed as it would be on a Roman or Byzantine coin.