I also am doing a pan drop soon and want to know where to find straight Dex III. No dex/merc, or does it matter?
Inconclusive auto parts store searches for "Dexron III": They all are either dex VI or a "multipurpose fluid"
Advance Auto Parts: Search Results for dexron iii
Search: dexron III | Transmission Fluid | AutoZone.com
List: Search for 'dexron iii' | O'Reilly Auto Parts