in Michigan - I am from Mich-gan, grew up there - I would run
Haidenau K66 as winter sole. I run them all year around on the Skorpion and they are great.
Haidenau belongs to Continental, so there should not be any real problem getting them. They are definitely worth looking into.
I would not ride them for that trip to Reno, tho.
I don't think I can recommend much of anything for a 5000ml (=8000km) trip which is more than just about any decent tire sold in Europe will even last.
Maybe the
Metzeler ME77, a classic wooden tire as we say over here, runs for thousands and thousands and is about a hard a piece of wood. Fine for an SR500 however, whose terrible handling makes you go slow anyway. I certainly would not ride it in the wet, let alone in the winter on my bike.