Searching for " sangita ratnakara english translation pdf " yields dozens of links. But most fall into three problematic categories:
A massive digital library hosting scanned, out-of-print editions of the Shringy and Adyar Library translations uploaded by academic institutions.
Sarangadeva composed the text at the court of the Yadava dynasty King Singhana II in Devagiri (modern-day Daulatabad, Maharashtra). The work is uniquely positioned at a historical crossroads, capturing the unified traditions of Indian music just before it split into Northern (Hindustani) and Southern (Carnatic) traditions.
As for an English translation in PDF format, I was able to find a verified source: