I think I understand. The difficulty is that for European registration in years past, Socata must have deleted the GPS NPA part from the KLN94 FMSup - otherwise it would be more difficult to get an FAA IFR approved GPS without GPS approach approval than with - because the standard IFR FMSup for GPS boxes since the KLN89B/KLN90 era includes GPS NPA approaches ie. to not be GPS approach approved but approved for IFR/BRNAV, your avionics people would actively have to delete the appropriate bit of the FMSup.
I was referring to N-reg retrofits done in the UK. I think the problem is that some avionics shops may be very familiar with installation/engineering approvals through having an in-house IA or using one of the many independent IAs/DERs to come in and inspect and sign-off work. The IFR approval is a specific process that requires the London IFO to approve the flight test and FMSup - and this is a more "obscure" step that they are not familiar with. But there certainly are UK avionics outfits who are perfectly familiar with the process.
BTW, the New York IFO deals with pilot licensing and operational approvals (eg. MELs, PRNAV) and the London IFO only with maintenance matters (I think it's there to mainly approve and oversee airliner maintenance). So as N-reg operators in Europe, one has little to do with the London IFO other than IFR approval.
rgds
421C
on EASA, I have little knowledge of the processes, but (apart from the major mod cost) I would be surprised if there wasn't a fairly straightforward EASA way of getting IFR and Approach approval for GPS. We may not have them in the UK, but GPS Approaches have been around in France and Germany for a while.