There are many multipage dialog scripts out there, including a couple of good ones in this LSL Scripting Library. This particular one, inspired by a user question in the LSL Scripting forum, is very simple. Aside from being fairly compact and easily readable, it has the advantage of never using more list memory than it needs for the 12 buttons on a single menu page.
// Simple Multipage Menu -- Rolig Loon -- August 2013
// The Menu routine in this script will parse your input list (gNames