I doubt you’ll find one using the normal channels.. Ebay or possibly amazon may have some options although as you said I’m not sure how authentic they are. You might have some luck looking on the for sale forum for a used one in good condition. You could also look into some of the the other case makers that offer leather cases, they may still have options for the SE..
eBay is fine if you pay with PayPal, as you are guaranteed your money back if it does turn out to be a dodgy transaction. You can usually tell by someones feedback or time trading on the site if they are out to rip you off and buying from actual businesses on there, and not from a private seller, gives you even more protection.