Strelok's PDA is not in Army Warehouses. Have you talked to the Doctor in Pripyat yet? He spawns after you find his diary in the Monolith "Church", Pripyat. Hint: His diary doesn't spawn until after you have completed NPP2, the regular ending in original SHOC.
He will tell you that you might find it in the Sarcophagus, but it's not there. You need to go there anyway, and read a note from Strelok.
The note directs you to the Miner, who will tell you where to find it.
Один выстрел один труп (One Shot, One Kill)