I also tried to find "native" combobox in Tk, asked on perlTk mailing list and failed.

Actually it was discussed in TCLCORE mailing list that most probably native combobox widget will be added in Tk versions 8.5.

Currently, in my opinion, most close behaviour provides widget "ComboBox" from BWidget package of Tcl/Tk.
There is no direct equivalent in perlTk, but it could be accessible via Tcl::Tk perl module (like any other Tcl/Tk widget).

However this will probably be not acceptable for you, as long as coexistence of widgets in perlTk and Tcl::Tk is currently buggy.

Courage, the Cowardly Dog