I have the same issue, blurry iron sights. Been looking for a new 1X scope cannot find one anywhere. Vortex and Sightron used to make one.
Vortex still shows it on their webpage but it doesn't seem to exist anymore:
https://vortexoptics.com/vortex-crossfire-ii-1x24-muzzleloader-riflescope.html
looked into other sighting systems:
Aimpoint has several 1X full size scopes:
https://aimpoint.us/shop-products/red-dot-sights/?sort=featured&page=2
Williams makes a special sighting system for muzzleloaders.
https://shop.williamsgunsight.com/ecommerce/p/western-precision-muzzleloading-sight-676584
I talked with a representative about it. The rear peep sight comes as a .150" diameter hole. It can be unscrewed and used as a ghost ring or three other sized peeps are available:
.125" .093" .050" The front sight is a globe with 10 interchangeable reticles.
As I understand it the correct sized peep hole can help with focus.
https://rangerpointstore.com/news/rifle-peep-sights-how-to-improve-your-vision/
Mk1 Micro SeeAll Open Sight
I know little about this.
https://www.seeallopensight.com/products/micro-seeall-open-sight