I imagine you can much more quickly/easily find information about crossover/storyline order from online sources than by searching through old copies of Previews. Just about every major storyline is going to have its own list on League of Comic Geeks or some other site (ComicBookReadingOrders.com?), if not its own Wikipedia page. Not to mention info printed in the books themselves.
Don't get me wrong - I'd be very happy if there were more scans of old Previews as well, but for your stated purpose, I think you can manage pretty well without them.
Granted, sometimes I think it's best to avoid certain orders, particularly those company-wide event orders. Reading the 6 issues of Infinity Gauntlet is a good read. Reading those 6 issues interspersed between the 40+ other issues in the crossover REALLY weakens its impact. Far better to read the main series, then read all of the crossovers afterwards, most of which only have the slightest of connections to the main plot.