Slings for just about everybody have dried up lately. Just a year or two ago I could pick up a "new" rifle, do a quick search on ebay and have it's correct sling on the way. Had a nightmare of a time the other day finding Spanish slings for less than $30. I eventually did but it wasn't easy. Carcano slings dried up about three years ago. I tend to grab a repro K98icon sling for any of the short rifles I get today. SA marked slings were pretty common for a while but they are gone also and wouldn't be correct for an 1891.

If you want an original sling, just be patient and do a daily search on ebay for them. One will most likely eventually show up. Just be prepared to pay roughly $60 for one.