Try these if you haven't
Pike County is definitely not on any kind of fancy trunking system. I've not been up that way much recently, but their primary frequency is 155.700 with a PL tone of 141.3. If your scanner can put the PL tone in I would recommend it as the Troy Police is on 155.690 and can bleed over onto 155.700 depending on where you are. The only other active frequency I've found for the sheriff is a repeated over in Clarksville. I do not remember that frequency off hand but I am sure it is in the database.
Keep in mind that Pike county is a very small county population wise and as such, there won't be a lot of radio traffic. In addition, you will only be able to hear the deputies if you are fairly close to them. If you want more to listen to in that area, you can add the Bowling Green PD (155.760) and Louisiana PD (155.010).
St. Charles, MO