Post 16, your pet spells become increasingly more difficult to find. Usually, only one or two per set are available on the standard merchants. However, as you said, there is a high elf spell merchant in the Ocean of Tears who sells some, though by the mid-20's you have to research them regardless. In the 40's, you can find many of your spells in the library in Katta on Luclin, then your lvl 50+ spells are drops (and I believe researchable).
My mage is only in her 30's but, so far, hasn't had a problem with research. I spend my training points to top it off, put on my Thoughtfiend Horror Scalp (+5% research skill, you can buy a quill that does the same thing for dirt cheap in the Bazaar) and have very few failures. I'll readily admit that having the money to buy up training increases is a big benefit, but I also have tons of lower level components I could be training on if I wasn't so lazy