On my 16 inch I simply have 16 inch snare wires (made for 16 inch snares). I bought them from a Dutch custom builder, he also sold me a thin snare reso head 16 inch. Wasn't able to buy those from normal company's.
I know pure sound or gibraltar make snares for 14 inch drums with extended snare mechanism, those are 16 inch long too.
Premier maybe (for their flobeam mechanisms?)
Craviotto makes 16 inch snare-drums. Also saw a youtube video with a 20 inch snare by Craviotto! Sounded pretty good!.
Maybe a drummer-friend is gonna give me a thick beech Sonor floortom shell 16 inch. Planning to cut 3 or 4 snare drums out of it, customize them and make some kind of business of it.