My local Home Despot carries Carlon Resigard, but not in the 2".
I just bought 2 50 foot coils of the 2" on Friday, from a local electric supply shop.
If you're very particular, you can research the Carlon Resigard options on the Carlon site, using their catalogs. Then order the specific parts anywhere.
If I were you, I'd physicially visit one of the local electric supply shops, after doing a little online research. Kindly ask to see the boxes, and ask for help with your project. Great, underutilized local resource, with competitive pricing.
I cut into the chase surrounding my fireplace today - huge, open space around the fireplace. So much space that I installed an access panel, in a master bedroom closet, that I can crawl through into the chase. I'm installing attic-basement conduit through this chase.
Edit - Blue 'smurf tube', flexible nonmetallic PVC conduit, will also work fine for your future wire runs, and is widely available. It's more expensive than the Carlon orange Resigard conduit.
Don't forget you'll need 110V to the display, also. You could install a recessed multi-gang box over the fireplace, combining 110V and low voltage into the same box. Example from Arlington:
I understand this doesn't help you with your conduit problem - just something to consider.