There are several tough ones, just wondering which issues would you consider "tough" or tougher?
31 is very tough. I've been the bridesmaid on that book more times than I care to count. 35 is about the same, but doesn't command as high a price.
Most of the issues between 30 and 37 are hard to get. 38 is easy. 39 and 40 are tough.
41-48 are easier but still desireable. 49 and 51 are easy-peasy, as are most issues to the end of the run. There was a warehouse find of 70s, so Vinny over at Metro probably uses them to line his birdcage and light his cigars. I don't see the last issue much, but it's out there.
Pre-30, most of the 20s (including 19, first Senorita Rio) are harder to find, but easier than the 30s. 29 seems to be the easiest. 20 seems to be out there, but not in higher grades. 28 is also fairly obtainable. I haven't looked much lately, but I don't recall seeing a 24 for sale recently. That may be my next stumbling block. The general rule seems to be that women in bondage are harder to find and if the woman is a nurse, the difficulty increases.
The first issue is easy, pretty much a matter of money. There's multiple issues out there for sale as I type. I don't know about 2-18 because I haven't been monitoring them as my focus until recently was on 19-48. I recall people here commenting that some of the issues are harder to find than others.
The Fight run should be a run that the average GA collector can complete because it has no Gerber 9s or 10s like Jumbo (or Planet?). The big barriers are 31 and 35.
All of this is pretty much off the top of my head. I invite others to supplement or amend this information.