I've always been attracted to the hard to find items. When this series first came out, the titles were very diffficult to find as Polygram was not distributing them through their normal channels. I had quite a time ordering them, I think the initial ones finally came through Tower and they had to get them from an independent distributor!
I am lucky enought to own the whole sereis, I made them a priority to purchase at the time.
You might find them by going to half.com, they are usually some of them listed there.
Should be a challenge to put together at this point, but worth the trouble.