I have never used a boat ramp right there, but here are some hints: 1) Pirates Cove is at the base of the bridge, there seems to be a ramp there, don't know if it is public accessable; 2) Deepwater Inn is also right at the bridge (I see a lot of fishing boats there and assume they would know a ramp close by); 3) Sport World Boat Center (573 374 9111) is right there; 4) Captain Ron's is a restaurant nearby that is right on the water, they might have a ramp; and 5) M&S Docks is in cove at the opposite side of the bridge from Pirates Cove (there is a resort beside them that might have a ramp).
I know 5-65 Marina (first lake road south of Greenview to the east) has a ramp, but that is a few miles from the bridge.
Sorry, no definative answer, but there are several leads...good luck...