re: "Do they publish lines per mm ratings for paper? "
I read that in order for an 8 x 10 print to be perfectly sharp we need to have 30 lp/mm. If the print has as few as 5 lp/mm it would be considered generally sharp for the casual viewer. Most of us probably like something in the middle and strive for closer to 30 lp/mm for perfect viewing pleasure.
To get that type of resolution at the 8x10 print level you need to get 200 lp/mm or more in a 35mm format. Hard to do. In a 4x5 format you'll need about 60 lp/mm in your neg which is quite possible and frequently achieved.
Color negative paper can achieve about 65 lp/mm and most quality B&W papers can easily go as far as 125 lp/mm. Even though all B&W papers are not equal, even with an average paper used correctly can easily reach 60 lp/mm , which is double the requirement to get crystal sharp prints.
If you are really interested in improving sharpness during the printing stage (aside from a very good negative, which is another topic) then your enlarger lens is the single most important element to consider.
The single simple thing that anybody should do is ensuring that your enlarger is properly aligned. The cost is only time and the improvement (if misaligned) is usually quite evident and a quick reward.
Hope this might help with your question. Sometimes folks seem to claim that one paper is sharper than another but I believe this is mostly due to other factors like acutance (perceived from the paper surface) and different contrast grading from manufacture to manufacture.