The two products David mentioned: the first has 4 photographic and 2 Bryce rendered HDRIs, see http://www.horo.ch/photos/hdri/html/hfurka_en.html,
The second has 5 photographic (one of them special) and 2 Bryce rendered HDRIs, see http://www.horo.ch/photos/hdri/html/hpfynjungle2_en.html
Then there are products with just one HDRI:
http://www.daz3d.com/shop/hdri-scene-files-2 has one indoor photographic HDRI (technical room).
http://www.daz3d.com/shop/hdri-scene-files-3 has one outdoor photographic HDRI (pond surrounded by trees), see http://www.horo.ch/photos/hdri/html/hsuome_en.html.
http://www.daz3d.com/shop/hdri-scene-files-4 has one outdoor photographic HDRI (arid alpine scene near a glacier), see http://www.horo.ch/photos/hdri/html/hplainemorte_en.html.
http://www.daz3d.com/shop/hdri-scene-files-5 has one outdoor photographic HDRI (open forest on one side, far mountains and a valley in the middle and background), see http://www.horo.ch/photos/hdri/html/hpreggontji_en.html.
Then, there is the Tourbillion series with one HDRI in each one:
http://www.daz3d.com/shop/tourbillion-chapel-hdri-and-scene-files (inside a chapel), see http://www.horo.ch/photos/hdri/html/hTchapel_en.html.
http://www.daz3d.com/shop/tourbillion-tower-hdri-and-scene-files (landscape as seen from a tower top), see http://www.horo.ch/photos/hdri/html/hTtower_en.html.
http://www.daz3d.com/shop/tourbillion-room-hdri-and-scene-files (in a ruin, half walls, half landscape), see http://www.horo.ch/photos/hdri/html/hTroom_en.html
http://www.daz3d.com/shop/tourbillion-garden-hdri-and-scene-files (some trees), see http://www.horo.ch/photos/hdri/html/hTgarden_en.html
http://www.daz3d.com/shop/tourbillion-dungeon-hdri-and-scene-files (inside a tower ruin), see http://www.horo.ch/photos/hdri/html/hTdungeon_en.html
The Deep Space HDRIs http://www.daz3d.com/shop/bryce-7-pro-deep-space-hdri-1 and
http://www.daz3d.com/shop/bryce-7-pro-deep-space-hdri-2 are partly photographic and partly Bryce made HDRIs
http://www.daz3d.com/shop/bryce-7-pro-advanced-layered-skies has a photographic HDRI (mountain pass), see http://www.horo.ch/photos/hdri/html/hsanetsch_en.html
These two products from David have a photographic HDRI each:
http://www.daz3d.com/shop/premium-rendering-hdri-ta-stoneheap has a photographic HDRI, see http://www.horo.ch/photos/hdri/html/hstoneheap_en.html and
http://www.daz3d.com/shop/premium-rendering-hdri-ta-2-rockfall has also a photographic HDRI, see http://www.horo.ch/photos/hdri/html/hrockfall_en.html
There are yet others, but I don’t remember exactly.
Now: generally, all HDRIs are in the angular map projection, Carrara needs them in the spherical/equirectangular/latitude-longitude format. You can transform them right in Bryce. Load the HDRI and Export it with the Filetype HDRI Image Files (*.hdr) and the Type Spherical. You can use that file as HDRI in Carrara.
If you only want the photographic background, load the HDRI in Bryce, click on Tonemap and export it as *.BMP, *.PNG or TIFF 24 Bits Per Pixel, Type Spherical. You can then wrap it on a sphere in Carrara. It will not produce light, it’s just a backdrop. If you want it correct, you have to mirror the exported image in a graphics application because the camera is inside the sphere and the picture is mapped on the outside. But this is only necessary if you want tho retain the original landscape. Nobody knows how it looks in reality anyway, so having it mirrored doesn’t really change anything.
There are some free, lower resolution HDRIs that come with the Bryce 7.1 Pro content. Try one or two of them to bring over to Carrara. Or generate an HDRI from the sky and export it to see how it works in Carrara. Once you see how it works, you may want to consider a purchase.
I hope no-one reading this post will be surprised when I recommend to just purchasing all the products to have the maximal choice of HDRIs