Online?

Not what you asked, but: There's a DVD with the whole thing in one package.

Also not what you asked, but maybe more to the point: There's not a major reason to watch the shows in order. Like virtually every sitcom of its era, there is no real "through-line" from episode to episode. Indeed, episodes are sometimes contradictory, and rarely, if ever, have any discernable temporal sequence.

The pilot is, perhaps, an exception, as it sets the premise (Jeff gone to Princeton), but that's hardly a complicated idea to grasp without seeing the pilot. Most people who saw it in its first run probably didn't see the pilot. Like a lot of pilots, it has some mild inconsistencies with the later shows. And the words to the opening song are different!

The practice of having plotlines run across entire seasons really didn't become prevalent until the '80s, I think. In the '60s and '70s, you'd sometimes get "two-part" stories that would run across two episodes, but those were considered exceptions to the norm.