Hi & welcome to ADISC I'm glad you enjoyed my story. Unfortunately I dont know of a way to sort by theme, some of the stories have tags which can be searched for but most authors don't add them so you may not find much.
Unfortunately I am much more of a writer than a reader and as such can't think of any stories similar to Natalie & Kim; one of the reasons I started to write is because I don't like stories that focus too heavily on AB, age-play & regression themes either & found there aren't a lot of these around. I have 2 more of my own stories, Ben & Jessica available on the finished stories forum which dont really involve AB/regression themes, as with Natalie & Kim they are about bedwetters and are fairly similar. I have other half-written stories which aren't currently on this forum but which I shall add once Natalie & Kim is completed as I'll be working on them next.
Sorry I can't be of more help, if I come across any stories similar to my own I will let you know