Where can I find covering for interior chimney hole???

Might go to an antique store and purchase a cover that was actually used to cover holes such as this years ago. Could really be a conversation piece.

It's hard to tell with such a close-up photo, but it seems like a framed photo or painting would cover it nicely.

if you no longer need the chimney I would fill the hole with fiberglass or some type of insulation. Next use a good grid type of cover ( used to cover holes in dry wall ) and then drywall plaster over that . you will probably have to do this several times because it will shrink into the hole . After you sand it and reapply the plaster a couple of times you should be able to paint it . We bought an old house that had one of these on the wall . Hope this helps

I think I would frame out a piece of half inch ply wood, attach attractive tiles, grout, and hang or mount over area under the mantle

https://www.etsy.com/market/chimney_flue_covers -or- https://www.ebay.com/bhp/chimney-flue-cover -or- https://www.amazon.com/flue-cover-plate/s?page=1&rh=i%3Aaps%2Ck%3Aflue%20cover%20plate . And just for fun, go here for inspiration: https://www.pinterest.com/bethintx12/flue-covers/

Great..I'm so glad you got something that will take care of it. Sounds like you have it covered!