There are 31 examples in the Beazley Archive database. The distribution is perhaps telling. Only one piece comes from Greece: Eretria on the island of Euboea. Eight leythoi have been found on Sicily: 7 at Gela, 1 at Selinus. A further example was found on Lipari. Two singletons have been found in southern Italy: at Paestum and Armento. A further example has the general find-spot of 'Italy' and another formed part of the Hamilton collection and probably came from the area around Naples. In other words, less than half the lekythoi have any sort of indication where they were found.
But what about the others? Some were collected well before the 1970 UNESCO Convention. Eleven do not have a stated source (some of those are recent, i.e. post-1970, acquisitions; others, such as in Berlin, Boston and New York, are older). Three surfaced through the Swiss market and one through a Swiss private collection. One appeared through Sotheby's in London, and another through Robin Symes.
I have commented on the intellectual consequences of such lost contexts for Athenian pottery before (e.g. the Sarpedon krater; the Berlin painter). Were any of the seventeen lekythoi without recorded find-spots found at Athens (or in Attica)? How many were removed from archaeological contexts in Sicily (or even Gela)? What about from sites in southern Italy?
Eretria, Euboea: London, British Museum 1899.2-17.3
Armento: Berlin, Antikensammlung F2205
Paestum: Paestum, Museo Archeologico Nazionale 4113
No place given: Paris, Musee du Louvre G381
Gela: Providence (RI), Rhode Island School of Design 25.078; New York (NY), Metropolitan Museum 25.189.1; Boston (MA), Museum of Fine Arts 13.189; Oxford, Ashmolean Museum V318; New York (NY), Metropolitan Museum 24.97.28; Gela, Museo Archeologico N67; Gela, Museo Archeologico N61
Selinus: Palermo, Mus. Arch. Regionale V668
Glasgow, Museum & Art Gallery, Kelvingrove 1903.70K
Naples, Hamilton Collection: London, British Museum 2000.11-1.38
Swiss market (3): Basel, Munzen und Medaillen A.G.: Bochum S1201; Shelby White collection; unstated ;
Swiss private collection (1): Bloomington (IN), Indiana University Art Museum 77.30.3
London: Sotheby's (1): unstated ;
Robin Symes (1): Fort Worth, Kimbell Art Museum: AP84.16;
Unstated (11): Malibu (CA), The J. Paul Getty Museum 83.AE.241; Geneva, Musee d'Art et d'Histoire 27810; Greek private collection; Wurzburg, Universitat, Martin von Wagner Mus. K1823; Berlin, Antikensammlung F2206; New York (NY), Metropolitan Museum 09.221.43; New York (NY), Metropolitan Museum 28.57.12; Providence (RI), Rhode Island School of Design 35.707; Hartford (CT), Wadsworth Atheneum 1963.40; Switzerland, Private ; Boston (MA), Museum of Fine Arts 10.180;