The only new Garrett is their pinpointer. If you want a new Garrett that goes really deep, you may have to wait awhile as they are tied up with govt contracts & such.
Looking back on the history of Garrett, they gone many years without a single new model, & some years they had several new models. I guess it's just whenever inspiration comes along?
If you would consider another brand there are new choices, from Fisher, Teknetics, White's & Minelab. In the economy range, Gold Century (made in China) has some new models.
I use a Fisher F70, very deep for $649 new (bought mine used). Many like it, some prefer something else.
Your GTA 500 would go deeper with a larger coil, a 10" Hothead for the GTAs or a Garrrett 12" Crossfire coil. HH, George (MN)