Hardware Sources

Spark Plugs
    Almost any plug can be had from www.sparkplugs.com
    NGK R847 - 8mm thread surface gap plug
    NGK R0045J - 10mm thread surface gap plug
    NGK ME8 - 1/4" x 32 plug designed for R/C applications

    AC Delco D514A aka "The LS2 Coil", a great coil with a simple interface, see the blog post
        available at Amazon
        with AC Delco 350R Wire
        coil terminal and boot for making single custom wires
    RCEXL - Small, lightweight, has a nice boot/wire system for the ME8 plug.
        Several versions available from Paragon RC

Machine Tooling
    Taps for almost any thread are available from McMaster-Carr, including 8x1mm, 10x1mm, and 1/4"x32

Raw Materials
    McMaster-Carr sells quite a bit, including high temperature 309 stainless steel
    Online Metals sells everything else