Anyone know where I can download older versions of Knoppix
Depending on how old a version you are looking for, my only guess would be to try all of the mirrors located at the following link: http://knopper.net/knoppix-mirrors/index-en.html You would have to go to each one and see what they still have available. It would require a little leg work, but I'm sure it wouldn't take too long. Some other distributions are based on older versions of Knoppix, like Knoppix For Kids, etc.
WaKa provided a solid link that has a few older versions. One of the mirror sites might go back even further. I have not looked in a while, but I'm sure you might find some older ones.
The main question would be why you might need an older version. They might be buggy and would not recognize as much hardware as current versions. If you are looking for something to run on an older machine, there might be a better choice with a different distro that requires less overhead, although the currrent versions of Knoppix will run on quite a bit of the older hardware. You might have to change to a different Desktop using a cheat code to get a little better performance on the older stuff.
ORICO 5 Bay Raid USB3.0 to SATA External Hard Drive Enclosure for 3.5'' HDD LOT
$140.79
ORICO 5 Bay Raid Enclosure USB3.0 SATA External Hard Drive Enclosure Up to 80TB
$135.99
3.5" Dual HHD RAID Drive Enclosure - Capacity 36tb with "0" RAID- 2.5" w/Adapter
$37.15
Dell EMC 092GD6 Broadcom 9305-16i LSI Quad Port 4 Port SAS RAID Controller
$84.99
ASUS Hyper M.2 x16 Gen 4 RAID Card- Used Working
$32.95
Dell PERC H330 PCIe 3.0 x8 RAID Storage Controller 4Y5H1 High Profile
$17.99
ACASIS 2.5/3.5 inch 2 Bay SATA USB 3.0 Hard Drive Disk HDD SSD Enclosure 4 RAID
$54.66
WD TB My Book Duo Desktop RAID External Hard Drive 0TB NO DRIVES
$42.00
OWC Guardian Maximus Raid Enclosure SATA Hard Drive FireWire
$36.99
CompUSA Internal 2 Bay Removable Rack for 3 SATA Hard Drives Raid Configurations
$25.00