TW 5500 is from TW graphics. My ink of choice for flatstock. We match by eye. They offer a set of pure pigment concentrates for this but no formula guide. I love mixing by gut and by eye so that's fine for us but yeah, if you are needing to match to PMS constantly you need a formula guide so, if that's the case, look into a similar product form Nazdar or someone with a formula system.
I can't remember if TW will mix PMS for you, they might, I would call and ask, really great folks there.