I recently attempted to get a firmware update on a old Garmin GPS150 TSO. (I see other POA members discussing similar issues) The avionics shop near me couldn't help, suggested I call Garmin. The tech at Garmin (nice fella - spent 45 minutes on the phone with me) confirmed what I alerady knew - Garmin stopped supporting the GPS150, GPS155, GNC250, GNC300 series GPS units a few years ago. He referred me to a Service Bulletin (which my local Garmin Dealer could access and download) which spells out the procedure to build a specal harness (essentially a serial port adapter) and download and install the firmware update. Unfortunately, Garmin removed from the actual firmware software from their dealer-accessable libraries - so even their dealers cannot download whatever the most recent firmware update was and install it in a legacy GPS unit. The Garmin tech suggested I see if I could find a Garmin dealer who happened to have saved the firmware update or patch. The latest firmware updates were issued sometime between 2014 and 2018(19?) or so, if they exist, hopefull they are not on floppy dics! If you hapen to have this illusive firmware in a folder in your Dropbox (or on a floppy disc) please help a guy out. If you have a one of these units and it's operating OK, please tell us which unit and which version of firmware you have running. Know a shop who has done this service for you - please pass it on. I know many of you (most) would probably suggest dicthing the legacy unit, but since my plane is over 45 years old (and I'm still using the venerable King KX-170B with success) it would be nice to keep the old (but much newer) Garmin GPS running. BTW, not trying to cheap-out here. I'm willing to pay a shop to do the job, if it can be done.