Reddit mentions of Sunset Amnesia Shooting Monofilament (Red, 15LB)

You can try making your own furled leader if that's what you prefer

I bought this level line I first started tenkara because it seemed like what most were recommending.

I don't fish tenkara much these days as I've fallen for euronymphing. However last summer, I had my tenkara rods on a family trip and no leader. I ended up just used this indicator line by Rio and it worked great!

Personally, I think any preferable size of nylon or fluoro will work for level line so long as you can see it. You probably don't need to spend $20 on imported, Japanese fluoro. I haven't messed around with it, but I could see Amnesia being effective as well