The stock shock spring on the Honda XR650R is rated at 9.3. Many riders will up the spring rate to 10 or 11 – but you should consult a suspension specialist to find the best spring rate for your weight and riding style.
Note sag is usually set at 100mm-110mm unladen depending on preferences.
There might be more – but as far as I know Percision Concepts is the only manufacturer of a Titanium spring for the XR650R rear shock. They’ll run you about $250. They only sell one size, a 9.x weight that is proper for a rider about 200 pounds.