Hand loading it is then!!

You have numerous choices in front of you.
I most strongly suggest the hard round ball, set either in shot cups or patched as is used in muzzle loading rifles.

If you choose the use of shot cups, get a mould that will cast roundball the same diameter of your choke.
Jeff Tanner will make you a mould for under $50USD and have it shipped to your door a couple weeks from request and payment.

You can use blackpowder or smokeless.
Loading them is about as easy as can be.

One of our members, Darryl, has had extensive experience with this kind of loading (extensive law enforcement firearms training, and big game rifle competition) and has coached numerous others here on the site through the simple and rewarding process.
The results are always fantastic!
What you'll get is a very hard hitting, very well performing, and consistent, accurate load that you've tailored for your own gun.

Think about it, and when you're a 'yes!!' to the concept, either speak up here in this thread, or start a new one and we'll all get together with you and make it happen.
You'll be happy with the results, I know it.

--Tinker