Here are links to a few previous similar question including how ot locate rider mower reopair shoips, and link to the John Deere website page to search for local JD authorized repair facilities.
https://answers.angieslist.com/need-j...
https://answers.angieslist.com/how-I-...
Assuming the blades are turning, just not as they should :
If you have belt drive unit, check that the belt is properly tensioned and not slipping - though if it does that for more than a few seconds you would be smelling burnt rubber.
If a hydrostatic unit, I would be checking the fluid level - low fluid level will result in lower power transmission - not to mention eventually overheating and smoking the unit. Very old fluid can also cause this as it breaks down and thins out. If yours has a hydraulic filter (most will) a plugged filter can also reduce hydraulic pressure, reducing power (and commonly also reducing drive system responsiveness/power).
Also check underneath for wadded up grass cuttings from cutting wet grass, or other foreign items cuaght up underneath which might be retarting the blade - either by the tips of the blades dragging, or because a plastic bag or rope or such is wrapped around the shaft and causing more friction there.
