I'm afraid there isn't any published limits, Lycoming are good like that.
Also what kind of oil sampling did you do? SOAP has kind of fallen out of favour, especially with modern fine filtration systems.
Do you conduct any oil filter debris analysis? I've seen some very good results on this, especially for catching cam follower failures.
On these engines (as with all aero engines, gas turbines as well) trending is generally better than go-no-go limits for metal in oil. Especially when you have the variables you get with Lycomings, normal, chromed or nitrided cylinders cylinders, what type of rings, OEM or PMA parts etc.
Think carefully before going over TBOs, they're conservative, but there for a reason. Ensure you have some kind of technical risk mitigation program.