Here's what I've managed to gather so far
Issue 171 (v25n1) Entry Page; New Spin of the Polyhedron; Five Foot Steps
Issue 172 (v25n2) Entry Page; Fight Against the Blight
Issue 173 (v25n3) Entry Page; Five Foot Steps
Issue 174 (v25n4) Entry Page; Foolishly Answered Questions
Issue 175 (v25n5) Entry Page; Digger's Union Revealed; Five Foot Steps
Issue 176 (v25n6) Entry Page; Foolishly Answered Questions
Issue 177 (v25n7) Entry Page; Five Foot Steps
Issue 178 (v25n8) Entry Page
Issue 179 (v25n9) Entry Page; Combat Medic; Foolishly Answered Questions
Issue 180 (v25n10) Entry Page; Magic of Eberron Preview; Combat Medic; Five Foot Steps
Issue 181 (v25n11) Entry Page
Still missing:
171 - Winter Fantasy is a Rap; People of Mind, Matter, and Radiance
172 - New Kid on the Block; Gnome Advice on RPGA Reporting
173 - A Death Knell Heard Across the Land; Beware Lords of Madness Approach
174 - New Kid on the Block
175 - So Many Choices
176 - Battle Hardened Diggers Part 1
177 - We Get to Play Too!; This One Goes to 11
178 - Combat Medic;
DM's Tools; Foolishly Answered Questions
179 - Origins 2005 Recap and Look Forward; Ready to Set Sail?
180 - Now Our Best Work Can Be Yours
181 - Underdark Review; Heroes of Horror Review; Foolishly Answered Questions
I also found a Foolishly Answered Questions columns that is not one of the ones missing from 171-181, so I'm unclear on whether it's unrelated or perhaps there are more issues. Dunno.
I have asked Paizo about it, as nearly all of the authors of the pieces were (and are) Paizo employees--they are a) wondering why I care; and b) perhaps able to find it...
Edit: Updated with two articles provided below.