Today I learned that Historic Enterprises, an American business that sells clothing and reenactment goods to medieval reenactors, has just started selling their own version of the Lengberg underpants. You can see the page where they're selling them, complete with a photograph, here.
Apparently their Lengberg underpants are being sold as one-size-fits-most. That might work fairly well, depending upon how long the ties are and how the cloth piece is shaped.
I'd be interested in hearing from any male readers who purchase the item and try it out as to its durability, comfort, and convenience factors.