Call a local glass shop. They deal with it all.

This isn't a difficult install, plus I've done it before, so I don't want to deal with a glass shop. Usually they don't do retail, but instead they want to do the install themselves, so I'd rather buy online.

Even with a frameless slider you need some sort of track or guide attached to the curb.

I don't mind attaching a small guide near the edge of the fixed door, just don't want a channel.

Designed properly, a channel is not ever visible. You don’t just glue it on the top. That’s an improper design. If you knew enough to design, measure, and order this correctly, you’d know that, and you’d know where to find what you’re asking for.