DVD help question

Hey everyone. So I never got a chance to watch this show so I'm a bit unfamiliar and in the dark, but I'm trying to get this answered with the holidays coming up. A family member is a huge fan of the original series and I wanted to buy them a few of the seasons on DVD. I've checked everywhere on Amazon and Ebay and can only seem to find it available as a complete $20 season pack over $100.

I know I'm sure I could find discs separately but would rather have new sets to give at Xmas. Does anyone know if separate seasons were ever available and if so where to find them?

Again I just wanted to clarify that I am only referring to the original 20 season series. Not SVU or any spin offs. Thanks