As has been noted earlier, no approach speed is published to a No Slat, Flaps 30 configuration. No procedure for a specific configuration usually means it's one that should be avoided. In this case, there are probably two reasons, both related to having a deployable leading edge device.
1) A deployable leading edge device allows the clean wing airfoil to be optimized for cruise. Using a steep flap deflection like Flaps 30 without the leading edge device extended for such a wing could result in a configuration that would have an abrupt leading edge stall and very nasty stall characteristics which would be difficult to sell to the certifying authorities.
2) A deployed leading edge device lowers stall speed by increasing stall angle of attack. If the leading edge is not deployed, the stall angle of attack at Flaps 30 may be so low that the corresponding operating speed to provide adequate manuever capability (even lower angle of attack) may make it difficult to land without having the nose gear touchdown before the main gear. Nose gears are not designed for this type of abuse.