I have just spotted this in an advert in the free GA Europe rag, by a well known firm - Harry M.
It has been a big thing in the USA for years, enabling one to buy certified avionics directly, for e.g. self installation, or installation by a freelance installer, without having to go through an official dealer for that avionics company.
The resulting cost saving can be massive.
The way it works is that new certified avionics is banned by most of the manufacturers from direct sales. It may be sold only via installers. This is to protect the dealer pipeline, for whom the ~25% discount on the supply of the hardware is an important revenue source, supplementing the amount they overty charge for the installation.
There is a lot of variation. The more obscure bits are obtainable direct, Honeywell/King stuff is pretty well uncontrolled (example), and at the extreme end you have Garmin who have a very tight control over their resellers.
Obtaining new Garmin stuff has been possible but only via subterfuge, usually involving a Garmin dealer who sells it "on the side". But nobody would do it openly. Presumably Garmin terminate the dealership of those who do.
But one avenue has always been open: selling into the US Experimental market, where self install is normal. These are advertised with a "cable harness" which is IMHO no more than lip service to the principle. You get an 8130-3 form anyway 
The European equivalent is the "light sports" (e.g. LAA in the UK) market.
I now see Harry M advertising some interesting stuff
GTN650 £6995
GNS430W £5995
with the "LAA harness".
An interesting development... this firm sells a lot of Garmin boxes so presumably Garmin are happy.
