Thanks lolypop000, but I need UK and ROI!
Meanwhile, I tried the "old style" method, as suggested by Rudy_P: downloaded MapReverseCoverter with mapsource 6.13.7 (from here: [Only registered and activated users can see links. ] - post #5), installed and "reversed" the maps, then unlocked with Garmin Unlocker ([Only registered and activated users can see links. ]). All perfect - my mapsource has now the newest maps!
Then, in mapsource 6.13.7 I've selected all the maps excluding nordic contries - Norway, Sweden and Finland (I don't need them!) - for reducing the map size under 2 GB (as my nuvi 350 can't read larger images) and sent them to the SD card. Finally, I unlocked the mapssupp.img on the card with Fast Image Unlocker 2.1 ([Only registered and activated users can see links. ]). Again perfect - I have a fully functional and updated gps!
Thank you for all, guys!