Bersa Thunder380 Holsters....
There are many holsters that are specifically listed for the Bersa Thunder380, but there have been a few that have been found to work fairly well.
One that I've found to do so is the Bianchi 19230, which is in the model 100 line. The holster is listed for the Beretta 84/85 series .380 pistols, which are somewhat similar in size/dimension. My(really my wife's as she "commandeered" it) resides in this holster and the fit is acceptable.
The main differences(in fit) between the PPK/Sig 230/232 and the Bersa and Beretta 84/85 F series, is the front of the trigger guard. The PPK's and Sig's have a rounded profile, while the Bersa(83, 85, 86, original 95 series and Thunder series) and Beretta F series .380's have the squared profile. The later Bersa 95 series(following discontinued importation of the all steel wide/high capacity framed .380's) have a rounded trigger guard profile, similar to the Walther PPK and Sig 230/232 pistols.
The short of it is, if you want a holster that isn't "made to fit" by one of the well known makers, in other words "off the rack/shelf", then look for one made for a Beretta 84/85F series pistol. Most times it will work okay. For better retention, go with a well known maker that molds specifically for the Bersa.