Neoprene socks is the only option for the big foot Seaskin, I would have opted for the socks even if there were boots available, they will easily fit your size 16. Pinnacle was the maker of the Hollis, look for those, I used an Aqualung neoprene bootie, something like ecozip(?) that also worked well. Once your feet decide to grow beyond size 13 it gets hard to find stuff.I know you're a big fan of the seaskin and it's gonna be my first dry suit when I save up the money for it. I have size 16 feet so I'm in a similar situation. It looks like the Hollis rock boots in size 14 and 15 have been discontinued. Did you just go with the neoprene socks for the seaskin? Looking through the options it shows 48/50 euro size is available in their tec boots which seems to be about 14.5/15.5 US.
Pinnacle make upto 15
Pinnacle Tecline Drysuit Overboot