I use the 40mm 120TPI version of the MSO tire and absolutely love it. Ive only used 3 tires on gravel bikes, so admittedly a small sample size, but I also figured I wouldnt look around since the 120tpi 40mm MSO offers what I want.

So a Raleigh bike(forget which) was spec'd with a 50mm tire called an LZY(i think) and it couldnt be found elsewhere online. Ends up Clement renamed it since it uses the MSO tread pattern.

The 60tpi version can be found here- Clément X'Plor MSO 700x50 - Black Mountain Cycles

I figured I would mention this because a quick google didnt bring much(anything?) up about the 50mm MSO tire- neither info about it or for sale sites.
Just happened to come across it while scanning thru the last couple months of blog postings by Black Mountain Cycles.

50mm MSO could be a whole lot of fun.