A few hours after I ordered a box of half-wide playing cards I realized I had the tools and materials to make my own.
I bought this 6-Inch Photo Bypass Trimmer ($(removed)) last year to make trick cards, and it was perfect for my needs. I used a pad of Post-It Notes as a stop so I could quickly cut the cards in half.
Once I was done trimming and cornering the cards, I had magically transformed one deck into two.
The face-down face is especially pretty.
Of course, I needed a box to hold the cards. But I could only make one half-sized box from the original box. The other deck will have to survive unprotected.