I looked at STC'ing (is that a word?) a complete flight deck for the 109E/S complete with digital autopilot, in partnership with a major avionics installer with EASA/FAA/TCCA certification.
He warned me it wouldn't be cheap. The parts came out at just under CAD$200k.
Plus SPIFR certification. For a market of less than 1000 helicopters. How many of you would be prepared to pay that much for better kit, fully certified? And yes we looked at Garmin too. G1000H at that time was not available to aftermarket, only OEM and Garmin didn't have anything else that was IFR capable for helicopters. Even the new G500H touch screen is 24k per screen and that is just for the screen, not for any of the adapters or other boxes to let it talk to anything else on your machine.
They know how small the market is. And it just isn't worth the hassle for them sometimes.
They also aren't as cheap as you would hope. I have personal experience with replacing the data card for the G1000H after the file was corrupted. The data card is needed for any software updates. Garmin were only too happy to supply a new USB stick with the file on it. For US$34,000.00. For a file. That they don't have to write specially. Just an off the shelf file.
And yet Garmin are eons ahead of Kratos for Customer Service!!!!
I'm still pushing for an STC with an avionic OEM (Astronautics) for the 109E/S to replace the Kratos screens. They're in final testing but it likely won't be certified till Q4/18 or Q1/19.
I feel your pain Dick and we've spoken many times about options. OEM's like Agusta/Bell/Airbus are contractually bound to purchase their avionics from the OEM. They can't shop around. But you can.
To a point. If you install an altimeter that is not listed on the Type Cert, you lose your IFR capability. Unless you submit a mod.
So gullibell, that is a nice altimeter there but you can't install it into a 109. Is it even the right size? 109 instruments are not 3 1/8 inch, they're 2 1/4 inch which makes them even MORE expensive.
The best advice I can give Dick, is let your fingers do the walking. Try these guys. They have feeds from many different sources.
https://www.avspares.com/parts/search?parts=3A432220F05
Good luck!