Getting a usable SSR is basically impossible and a pipe dream. Start a party if you get one.
Focus on getting usable Rs (which are really cheap to max) and usable SRs.
Something like these? ^^
I've actually gotten a lot more drops from farming R4s than from when I was still farming R3s. Feels to me like you just get 2 shots at getting one instead of just 1 in R3.