Originally Posted by
HillRider
Those plastic under the bottom bracket shell cable guides were included with every Shimano group. Check with any reasonably well established bike shop which should have a bunch of spares and you should get one at negligible cost. The attaching screw usually comes with it but, as noted, if your shell isn't drilled, double face tape or contact cement will hold it in place just fine.
Using rubber cement applied to one surface and pressed together while wet will hold sufficiently well and be easily removable. Or drill the hole and apply paint to inhibit rusting if steel. It might stay put by itself when the cables are under tension but securing will make things go easier.