There are quite a few good ones around the L.A. area, although you really do have to go outside of the city proper to find ones that aren't extremely specialized. This weekend we were in Dave's Olde Bookshop in Redondo Beach and Book Again in Torrance, where I snatched up a hardcover copy of Dear Laura: Letters from Children to Laura Ingalls Wilder for the embarrassingly low price of $5.00.
Laura began writing down her memories and stories late in life, and to her great pleasure, her books were received with an outpouring of enthusiasm from children and adults alike. She received many, many letters from her fans and kept a fair number of them in her personal belongings, and a nice selection of them are presented in this volume.
My favorites include poems written on lined school paper, valentines adorned with stickers and doilies, crayoned drawings of scenes from her books, and one enterprising teacher who even had her students fill a whole autograph album with messages for their beloved author.
I believe the book is out of print, but still available through libraries and secondhand dealers. It's a treasure for anyone who loves Laura, or who appreciates the charm of written correspondence.