What exactly do you mean "not present"? As in, it's not where the wiki says it is. If so, make sure it isn't a random spawning item. If it isn't, then I assume it's a glitch.
Then it probably isn't set to appear in the same place everytime. If you want a ring to resist magic and don't have high enchanting skills, try looking for it at Radient Raiment. It's a clothing store in Solitude that sells a lot of enchanted jewlery. If it doesn't have it the first time you check, you can try waiting 48 hours and they should have new stuff.
I bought a ring called ring of Magick Abatement, resits 45%(I think) of magick effects, I think at Radient Raiment.