It's not that much of a challenge. Just look for "job lots" on ebay. This is a good way to get multiple ones at once. And as for "new like looking condition", all they can do is yellowing, but that rarely happens. I've not yet seen a CD-ROM drive with any signs of wear; I mean, some dust aside or dirt you can just wipe off.
I would try to get a drive as slow as possible. 8x is probably already starting to be too much for a DX2/66, depending on the interface used for IDE (VLB/PCI is fine, ISA is not). Issue is, if the CPU can not handle the data as fast as delivered by the drive, the CD will constantly spin down, up, down again and so on. That makes it slower than using a 4x.