For purely informational purposes, you could check out metal-tracker. It's primarily a metal tracker (duh) but there are other genres there too but not as much of it. It's Russian site, but they have an English version. They generally have quality files, including FLACs and quality MP3s.
Alternatively, if those artists have bandcamp pages, you can use youtube-dl to get the highest quality they've uploaded there. Also, Bandcamp has the best artist cut so I recommend you buy music from there. On the first friday of the month, Bandcamp waives their normal cut and all of the profit goes to the artists. And through Bandcamp, you can actually download the files and keep it unlike some other places.
While FLACs are higher quality, they take up a ton of space. I have the discography of Blind Guardian on my hard drive and it takes up 10% of the total space despite being one of hundreds of artists with a similar discography size. So be wise with how you allocate your disk space.