Aristeia Needlepoint in Los Angeles has many talented stitchers among their staff who specialize in writing stitch guides for Melissa Shirley canvases. They've added a page to their website that shows a selection of the guides available from the shop with a purchase of the canvas there. They will do a guide for free for a canvas purchased at the shop but there is a charge for a guide done for a canvas bought elsewhere.
There is no price list for the guides. The ones shown are from Wendy Harwood and Laura Taylor but I believe they also sell guides by Beverly Churchfield.
UPDATE: Melissa Shirley has added profiles of all the stitch guide writers for her designs. Here is Wendy Harwood's--
Here is Beverly Churchfield's--
Here is Laura Taylor's--