I'm trying to develop a plot were a cult leader is trying to become a lich. Do any of the currently published D&D 4e books provide any canon for this?
Open Grave is your best reference. It doesn't contain any mechanics related to becoming a lich, but the first chapter includes a section on how undead are created. It's also got rules for grafting undead parts onto yourself, which might prove useful.
Revenge of the Giants features the legendary lich Acererak before he became a lich. You can gain some insight into the process there, although it's not worth buying the book just for that one bit.
The Dungeon Master's Guide includes a lich template on page 179. You'd probably want to apply this template to the cult leader if his or her plans succeeded.
Here's the Lich Transformation Ritual from the WotC compendium.
In D&D second edition, Enciclopaedia Magica has all the rules for the ritual to lichification. I guess also Van Richten's guide to the Lich might come in handy, if not for the rules, at least for fluff :)