The MIBs involved may vary, depending on the hw and sw flavor of your devices. You need to determine that from the Cisco Feature Navigator for your gears.
For cbQoS and cat6k "swouters", I used CISCO-CLASS-BASED-QOS-MIB and a lot of the following MIBs for :
"cbQosCMPrePolicyPkt" "1.3.6.1.4.1.9.9.166.1.15.1.1.2"
"cbQosCMPrePolicyPkt64" "1.3.6.1.4.1.9.9.166.1.15.1.1.3"
"cbQosCMPrePolicyByteOverflow" "1.3.6.1.4.1.9.9.166.1.15.1.1.4"
"cbQosCMPrePolicyByte" "1.3.6.1.4.1.9.9.166.1.15.1.1.5"
"cbQosCMPrePolicyByte64" "1.3.6.1.4.1.9.9.166.1.15.1.1.6"
"cbQosCMPrePolicyBitRate" "1.3.6.1.4.1.9.9.166.1.15.1.1.7"
"cbQosCMPostPolicyByteOverflow" "1.3.6.1.4.1.9.9.166.1.15.1.1.8"
"cbQosCMPostPolicyByte" "1.3.6.1.4.1.9.9.166.1.15.1.1.9"
"cbQosCMPostPolicyByte64" "1.3.6.1.4.1.9.9.166.1.15.1.1.10"
"cbQosCMPostPolicyBitRate" "1.3.6.1.4.1.9.9.166.1.15.1.1.11"
"cbQosCMDropPktOverflow" "1.3.6.1.4.1.9.9.166.1.15.1.1.12"
"cbQosCMDropPkt" "1.3.6.1.4.1.9.9.166.1.15.1.1.13"
"cbQosCMDropPkt64" "1.3.6.1.4.1.9.9.166.1.15.1.1.14"
"cbQosCMDropByteOverflow" "1.3.6.1.4.1.9.9.166.1.15.1.1.15"
"cbQosCMDropByte" "1.3.6.1.4.1.9.9.166.1.15.1.1.16"
"cbQosCMDropByte64" "1.3.6.1.4.1.9.9.166.1.15.1.1.17"
"cbQosCMDropBitRate" "1.3.6.1.4.1.9.9.166.1.15.1.1.18"
If your qos policies happen to choose not to utilize any "drop" action, you'd obviously be coming up empty with all the cbQos*Drop* OIDs, as I found out.