For the PSA AR9 with the KynSHOT AR 9mm Heavy Damped Buffer, these JP Enterprises Tuned And Polished Buffer Springs for .308 rifles could work. However, I recommend using one of the Blitzkrieg Components Sprinco Power Buffer Springs which are recommend for use with the KynSHOT AR 9mm Heavy Damped Buffer. These springs can be found at the link below.
https://www.opticsplanet.com/blitzkrieg-components-sprinco-standard-power-buffer-spring-ar15-carbine.html