I could recently buy two long 9mm barrels (170mm and 200mm) for the Pistol 06/29 made by the Waffenfabrik Bern (W+F).
I suppose they were produced, when the Swiss Army conducted trials with the 9mm Luger cartridge during the 1940's.
The W+F also produced 9mm Pistols 06/29 for the commercial market, but normally with 120mm barrels. These pistols are quite rare.
Better known (but also rare) are long barrels variants caliber 7,65mm Luger - some of these pistols were produced for sport shooting.
It would be fun to transfer an ordinary Pistol 06/29 in a 9mm "LP 06/29"...
Alexander