Try a custom leather smith. There are enough around on the internet, and even some that reside in certain gunshops (I'm thinking Guns & Leather in the Springfield, TN / Nashville area). Good leather is worth its price
I have a Desantis black leather speed scabbard without a retention strap that I use for my 686P 4". It's a pancake holster and retention is great. I use it for winter carry of my 686P under my winter coat. Desantis makes other good leather holsters for the 686 and 686P, you can find all of them on their website.
I've got a 4" 681 (same gun - no adjustable sights). I was looking for a IWB holster recently too and found one at Hoffners that looked promising. I was going to get it, but ended up spending the money on a M&P .40
Hope this helps with your search. Sorry I can't post the link. I haven't posted enough yet.
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