Following the question here (the answer to which may be “Yes but nobody will install it for you, so the market is tiny”) there are various sites such as Porcine Associates who make all kinds of strange boxes.
My view would be that with homebuilts, especially higher end ones, moving to glass, the demand for bits like this is small. Just as has happened in the certified scene where Davtron etc are almost nonexistent in new aircraft.
I am designing a “comms box” which can work as a programmable protocol converter, with some analog interfaces.
The Porcine page has been last updated in 2002…
Homebuild market has evolved from this time. Or build a very cheap one and then you go for the round gages and with just a COM if really needed. Or you build a serious plane (RV type) and then you will go for glass with integrated autopilot. If needed, you add a Garmin/Avidyne navigator.
I did realise it is very old, but there are many niche businesses which sell old stuff. My own business sells even older stuff than this one