The GNS430 is compatible with many CDI's on the market. There is a
requirement around the annunciator for the CDI itself where the user needs
to know if it is tracking the GPS or the VLOC (NAV). The 430 has an
indication on its display which may satisfy that requirement, I'm not
sure.
The Garmin GI-106 CDI has it on the CDI face as well but the unit will run
you $1,100+. There is also an electronic CDI on the default NAV screen but
that of course has no glideslope.

The CDI on the GNS430 screen only shows GPS. It does not ever show VOR or
LOC deviation. The annunicator in the bottom left corner of the screen
which says either GPS or VLOC is there to tell you what the external
mechanical CDI is showing.

You wouldn't believe how many 430 users out there still think they can
follow a VOR based course deviation on the unit's display.

As long as the 430 is mounted in the radio stack near the flight
instruments, you don't need to install an external annunciator panel.