Non U-Lock that can be mounted for carrying?
Any specific lock recommendation is going to be out of date in a year, so I'll focus on identifying the best kind of lock: 

Any cable locks are going to be insecure by nature, but it's unfortunately the only other kind of lock available just now. (I'm not counting big-ass chains with giant locks; those are more for show than for security.) 

One of the heavier Kryptonite cable locks is probably your best bet. To beef up the security, I'd get two of them and lock up different parts of the bike. I'm told that keyed locks are harder to crack than combination locks. 

However, have you considered getting a smaller U-lock and a long cable? You'd get the best of both worlds that way. Since places to lock up are scarce, you'd usually end up using it as just a cable lock, but it'd give you flexibility in the event you find a good sign or bike rack. 

Bike mounts: These tend to fall apart rather quickly. I recommend focusing on a small pag to carry your locks, rather than use a frame mount. There are triangle frame bags and small trunk bags that do the job nicely. However, cable locks have a great advantage over U-locks--you can coil them up and hang them from your handlebars. Unless you have smaller drop bars, it's amazingly convenient.