La Bella makes a set, but there are others as well.
If you want nylon, before you calculate string diameter, you need scale length and desired tuning. Also, are you playing fretted or fret free banjo? This will make a difference.
The LaBellas are a little loose for my taste. You might want to call the Music Emporium or vist the web site at www.themusicemporium.com. They offer three different nyllon sets that should suit your needs. But know your tuning and scale legnth first. I believe these sets are English and of very high quality.