The page for spice models of valves/tubes has now been split into the following pages

• Rectifiers
• Triodes
• Pentodes/Beam Tetrodes

Further models can be found at Norman Korens site.

Also check out the section on using Vacuum Tubes with PSpice which explains how to draw the symbol you require and make use of it with the models on these pages.

For LTSpice users, there is a page on using vacuum tube models with LTSpice.