Interesting idea, but the spells that have a name are a fairly random list - and some of them are very evocative and fun. If you go this route, do keep in mind that denial of player desires has a negative impact. When you tell them no, it has a cost.
In my setting there is a book called (boringly) Librum Magicum. It is a well known text and is available in almost any place that deals in books. It contains descriptions of every spell in the PHB, every monster in the Monster Manual, and every Magic Item in the DMG. It doesn't include mechanics, but each thing gets an entire page. In the case of spells there is enough information that PCs can 'learn' the spell (via class mechanics) for sorcerers, bards, etc... Wizards still need a scroll or spellbook to copy in order to learn it.
Spells from secondary sources (other WotC books, 3rd party sources) are 'known of' from legends and stories. The same goes for monsters. There isn't detailed information available, and you have to ask the DM for them.
In terms of the 'unknown' monsters, magic items, or spells - I use homebrew materials. I have thousands of spells, magic items and monsters that I've collected over the 4 decades I've played. These represent about 30% to 50% of the things the PCs encounter. I have a few monsters, such as my Axemorph Demons (based upon the figures from the Dreamblade game WotC made), that make a lot of appearances. I have a few that appear at least once a campaign as inside jokes (Bunny Fish - which appear to be 'half bunny, half fish' meranimals - but are actually the 'missiles' sent off a near stationary bottom dwelling sea monster that essentially blows up large sea creatures and ships and then slowly eats their carcasses). The spells I have come from older editions, from original creations, and from other games in which I played. I usually have to tweak them to update for 5E, but surprisnly not too much.