Does MR have an online archive of all issues? If so, is there a way to find info on any given topic?
No. They do have an index of all issues and you can order articles but the magazine itself is not on line.
Tom
It may not work for all articles, but a google search has helped me find and print some of the specific articles I needed. You need to know the correct title and date.
There is an index of articles for a number of railroad magazines at
http://www.index.mrmag.com/
However, the acutual articles are not available. It may help with doing the google search by providing the correct title and date. Also useful if you have or can get to the original magazine.