There is nothing too much like Star Wars Saga Edition. Luckily, getting a copy really shouldn't be that hard, they are at used bookstores in my area at least.
Are you looking for system or setting similarities?
SW:SE is a d20-based game. It is not d20 Modern based, though depending on how close you want it, d20 Modern + d20 Future provides a somewhat similar play experience (more similar than using GURPS or Savage Worlds, I guess).
Wizards talked about both SW:SE and the 3.5e Tome of Battle as being 4e progenitors but I don't see a lot of similarity. I liked both of those and played a good bit of ToB in 3.5e but hate 4e; perhaps it was "inspired by" them in a high level sense but there's not a lot of mechanical similarity.
The (much older) West End Games d6-based Star Wars had many, many books worth of support with setting, adventures, etc. It shares zero mechanics with SW:SE - it's a previously licensed game by a different company using a different system. It is really good though, and the rules are free now as d6 Space Opera (without of course the Star Wars intellectual property).
There are the new Star Wars games by Fantasy Flight Games, which are of course set in the Star Wars universe, but are completely different than d20 system-wise.
If you want it science fictioney, but d20ey, you could look at d20 Traveller. It's a pretty bad d20 adaptation and not really a great intro to the Traveller universe, but depending on your values and personal initiative that may or may not be a deal killer.