Is the level 24 Necro pet spell still research only?

Yes

Words of Transcendence are for the mage summon stack of food/water spells and were kinda rare iirc, I think I had to buy both from players.

Mages have to chain research for some of their 49 pets, so they need extra Words of Convocation and Incarceration. These words are also kinda of rare, so they can be valuable. They're mid 30s to 40s.

Necro research in general is pretty common, however a desperate necromancer may buy Words of Allure, Words of Detachment, or Words of Possession for their 24 pet.