Congrats on the 3913. Possibly the finest 9mm single stack carry gun made. By anyone. My friend Jeppo is correct. I carry one. On those days I carry a 9mm.
Being left handed AND carrying an out of print gun, I have searched for holsters. Ebay and Gunbroker have yeilded a few. Murphs holsters China Grove makes a belt slide for a Colt Defender which fits my 3913 like a glove. He use to do all the gunshows, back when we had gunshows. Greensboro Guns and Ammo stocks some of his holsters, but I don't recommend that shop.
As far as Kydex, I only have one. Made by Blade Tech and I don't 4hink they make it any longer. Watch Dog Tactical in Charlotte will make you a holster, but you will need to bring them the gun.
Don Hume made several nice 39XX series holsters and still has a few. I have a belt slide with sweat shield - H721 NO28-11.
And I have found that any holster for a 6906 will fit the 3913 as well. Non fitted leather holsters for a Sig 239 will work as well. Even some 5906 holsters will fit. And of course a few leather holsters for a compact 1911 fit too.
Good luck! It is well worth the search for such a fine carry gun. Hope this helps. Regards 18DAI