This originally appeared in the May/June 2002 Enigma; many thanks to Hot and Trazom for their editing. The abbreviations 10C and NI3, as usual in the National Puzzlers' League, refer to the (Merriam-Webster) 10th Collegiate and 3rd New International Dictionary.
In this puzzle you must search for the central figure of 6A 39A. Before being entered into the grid, several answers must be altered so they constitute 6A 39A. The initial letters of the corresponding clues (in clue order) will spell the name of a place where the person you seek might be but currently isn't. If you take additional clues that indicate that same location (in a similar but not identical manner) and string their answers together in the logical way, you will find the current location in which your quarry resides.
ACROSS
1. Support poles within track
6. See instructions
10. Actor Sidney is less smooth when nameless
11. Acme copier precedes Xerox's first unit
12. Glen meets Egyptian deity and Irish politician
13. Consul furtively hides brimstone
15. War god turned small with time
17. Fish seems to be headless
19. Job-seeker from Long Island is able to get inside appointment
21. Frequently pertaining to a minyan?
23. Small spot is unfortunate
25. Golden city of antiquity seized by reactionary spy group
26. Albert has hesitations about elected foil, perhaps
29. Tears apart epitaphs
31. Came in second place against a real Dacian tribesman [NI3]
33. Buffalo are in it to provide stability
36. No one assumes instrument to be crescent-shaped
37. Throw strip of wood
38. 007 embraces lady that is Dagwood's wife
39. See instructions
40. Missouri gals with rum, initially
DOWN
1. Starts soaring at top speeds
2. Engine fuel to get around sun and earth
3. Upset Connery with denials of Scottish character [NI3]
4. Something groovy follows street parade
5. Perp destroyed fabric
6. Stripped stolen sheet metal
7. Kingsley chases after Michigan tribesmen
8. Lot: an evil grasper in flight?
9. He gets in back to try again
10. Lamp fuel a mouse overturned around Quip
12. "Ottawa's leadership is buried in vice," April fumes
14. Final union left vacuous one with spouse
16. Confidence game by quiet rogue
17. One cutesy-sounding case
18. Lacking water to submerge copper safe
20. Step around energy plants
22. Black gum is strange to Lupe
24. Got lid translated, being bilingual
27. Bachelor times are essential to liberation [abbr., 2 wds.]
28. Referring to a person, place, or thing currently insignificant to the
listener [NI3]
30. Tree is around to act as roughage
31. One cube for Ms. McDowell
32. Heard vessel is useless
34. Vessel without prow!
35. A storyteller cut short other items in Latin [part of 10C phrase]