Q. How can I find John Calvin's commentary on the Psalms?

The best way to find Calvin's comments on different scripture passages is to look through Calvin's Commentaries.

Calvin's commentary on the Psalms is available at the Fuller library under the call number BS491 .C168 v. 4 (parts 1-5). 19th century English translations of Calvin's Psalms commentaries have also been digitized by the internet archive collection of public domain works. Complete is the 3 volume edition printed by Talboys: London, 1840. 

Vol. 1: Psalms 1- 46
Vol. 2: Psalms 47- 100
Vol. 3: Psalms 101-150

Additionally, you can look through the index of biblical passages in Calvin's other writings to see if he references a particular passage. While it does not currently include Calvin's commentary on the Psalms, the full text of many Calvin writings in the original French and Latin are available through the Calvin and Geneva 16 Database.