I'm not sure exactly, but I'm certain it'd take at least several hundred skill points into magic finder for you to get "a good chance" of finding the RoL. 12%chance? From the original 0.01% chance? Well, I don't know exactly, but I'm certain nobody's ever going to use that much skill points onto magic finder just to find an RoL; by the time you got the skill points needed to do so, you'd be far beyond Sarumar's level...
But let's take some calculations.
Each point in magic finder increases your chance of finding non-ordinary items by 50% of the original chance.
Therefore, 1 point in magic finder = 0.015% chance.
2 points in magic finder = 0.02% chance.
..... and so on, and so on, and so on...
By the time you reach your targeted chance (12% chance) you should be at about: 12 divided by 0.005 = 2395 points in magic finder. That's more skill points than Sarumar has in levels
.
However, alternatively, if you interpret magic finder differently, that it is compounded:
1 point in magic finder will still mean 0.015% chance.
but 2 points in magic finder will mean 0.0225% chance.
3 points will mean 0.03375% chance... and so on.... and so on... and so on.
Your target, 12% chance, is still a long way off, but it is far easier (if still impossible in one lifetime) to attain.
By the 18th point in magic finder, your chance of finding an item should be:
14.7789188......% chance.
To get 18 skill points still requires 72 levels, however, and that's assuming you never put skill points in anything else as well as magic finder may be compounded. I'm thinking it is not compounded, but I have no proof of that.
Edit: Added calculation methods:
For method 1:
(12 -0.01) divided by (0.01*0.5)
For method 2:
I had to use trial-and-error to get to the right amount:
(0.01)*1.5^(18)=14.7789188......