With the introduction of the sabot and modern bullets gun makers were not seeing the demand for the .54 caliber barrel as much. Granted when we were shooting roundball and big conicals, .54 calibers in traditional rifles were very common. Knight and Thompson Center both used to make .54 caliber inline as did CVA and Traditions. But IMO people went to the .50 caliber with the modern projectiles and found they could do the same job as the .54 caliber could with the older style projectiles.

Now there are .54 caliber inlines. I saw a System One on the auction site the other day with a .54 caliber. Still if I were going to hunt elk, I would use my White Rifle in .504 (and White does make a .54 caliber that throws chunks of lead also) and a big conical. Those that have elk hunted with the White claim no problems in planting elk with them.

If you can not find one for your Encore, there is always the chance for another rifles... like a White.