I have foraged through the internet to no avail.
Is there a way to systematically check if spectra from a given exoplanet has been reported, like a catalog or list of references, or is a literature search using likely keywords the only way to look into this? Thanks!
For an authoritative source of data on exoplanets, your best bet is the NASA Exoplanet Archive. Their page for HD 219134b is here.
For planet spectra, the archive has a page for planets with transit spectroscopy, but searching that page for HD 219134 yields no results. Note that transit spectroscopy is challenging, so there aren't very many planets to which this technique has been applied.
In general, if you want to search for literature data on a particular astronomical object (whether it's an exoplanet or not), two good bets are NASA ADS or Simbad. For ADS, you would type object:"HD 219134b" in the search box. For Simbad, you would do an object search for "HD 219134b", and then scroll down to the "References" section and click "Display". The advantage of both of these types of searches over a general web search, or even a general database search with that string, is that different names for the same object are cross-indexed; for example if you searched one of those for "alpha Ori", you would also find papers that only used the name "Betelgeuse", and vice versa.
