Are they difficult to find? I have them all (of the original 20). After #8, I believe, I started collecting two copies of each - one for reading, one for bagging. They're on my list to sell, but I'm slow to get going on the selling thing.
I also have the second portfolio - 8 portraits of the main characters.
It's a bit baffled me. I loved them then, and I still like the story, but I don't feel really compelled to keep them. On the other hand, they don't appear to be worth a whole lot.
The first prints of 1 though 7 are harder to find but none of them are impossible. Buying them on ebay is a bit tricky due to the number of reprints the early issues went through.