Custom doors from a cabinet maker. In fact the total built in is from a cabinet maker since the doors and drawers are inset.

https://www.durasupreme.com/door-styles/mullion-doors#.XgKGXEdKiUk

Many closet type companies can do this type of work. We used Stor-X for our master closet, mud room, laundry room, and have a quote for office built ins. Where we live they are a company similar to California Closets but at a more cost effective price point

Custom doors any door maker can do or just get plain unpainted doors and ask your cabinet maker to add the trim. I actually love Pax from Ikea the storage is awesome but does lean to a more contemporary style I did have a client where we had the cabinet maker design a built in to very exact storage needs and it is beautiful , not cheap, but beautiful. So make sure what you have can be stored properly function first .

Helen

As others have posted, this would be a very easy thing for a woodworker to accomplish

I recently finished a remodel and all of my cabinets and doors have this kind of detail. It's just applied to whatever plain door you select. It is less expensive than purchasing the style from the door store or cabinet store.

For example, if I had purchased doors with molding and Lamina from the door store the cost would have been much more than purchasing a plain wood door and having a local tradesperson replace the wood middle section with Lamina and then apply molding in the style of my choice. My design is geometric but one could have any design done using the same construction techniques.

Bedroom door with Lamina and applied "moldings"

Not identical but these are all "moldings" applied to the plain wood and glass. They could have been any design including the curved that you posted.