You have a wide variety of search coils to choose from.
Any of the CX series of search coils will work.
The 4.5" Crossfire (NOT CROSSFIRE 2) Super Sniper will be the smaller search coil that you want.
The stock CX search coil is 7"x10" Elliptical Concentric Rhinotough. This one replaced that 8.5" Crossfire that you have as the stock search coil years ago.
Actually, none of the CX search coils are made anymore, but you can still buy them brand new at KellyCo or Garrett's or any number of dealers have them in stock.
Other available search coils for the GTAx1000 are the 12.5" round white Crossfire(which is actually hard to find now as they are no longer in stock and mostly found used. Also the 10"x14" Power DD CX series works, but it makes the detector really front heavy.
Oh yeah, and there's also the 5"x10" DD Crossfire and 3"x7" DD Crossfire, but they are rare and hard to find.
You can get the owner's manual online at the Garrett website. Also, you can read the field test reports for the GTA 1000s on the Lost Treasure magazine website.
Best of luck to ya.
Happy Hunting.