Does anyone know of:

A: A Game system

and

B: A Miniatures range

That would allow you to play a tabletop wargame, pitting Empire and Rebels against one another, in the vein of Warhammer 40k, or similar?

Scale not really an issue, but 28mm would be nice, but smaller or larger would be fine.

Not a Boardgame as such, a proper skirmish system.

I dont know if anyone has any licence to create 28mm wargaming minis in the Star Wars style, but a game system could be converted with effort (unless one exists)

RD

http://starwars.wikia.com/wiki/Star_Wars_Miniatures

FFG produces 3: X-Wing, Armada, and Imperial Assault.

https://www.fantasyflightgames.com/en/products/star-wars-imperial-assault/

Kind of board game meets tactical simulator.

http://www.starwars.com/news/the-big-impact-of-west-end-games-star-wars-miniatures

Old School, closest thing you'll find to 40k Star Wars other then fan-made stuff.

Good news: The rule books are easy to find. The system is pretty easy to learn. The Heroes are compatible with the WEG RPG system so if you play that you can actually import the players into the larger battle.

Bad News: WEG miniatures are hard to find (WotC ones are easier, but the scale will be a little off). Also the System handles Droids similar to hero characters, so no "true" battle droid squads. Game has more in common with the D6 RPG, so larger battles can take a little while. Decent running 2-3 squads of doods per side with a speeder or two supporting, but if you want more of a 40k 4 squads, 3 heroes, 4 vehicles per army in a single battle you'd better clear some time.

http://www.starwars.com/news/the-big-impact-of-west-end-games-star-wars-miniatures

Old School, closest thing you'll find to 40k Star Wars other then fan-made stuff.

Good news: The rule books are easy to find. The system is pretty easy to learn. The Heroes are compatible with the WEG RPG system so if you play that you can actually import the players into the larger battle.

Bad News: WEG miniatures are hard to find (WotC ones are easier, but the scale will be a little off). Also the System handles Droids similar to hero characters, so no "true" battle droid squads. Game has more in common with the D6 RPG, so larger battles can take a little while. Decent running 2-3 squads of doods per side with a speeder or two supporting, but if you want more of a 40k 4 squads, 3 heroes, 4 vehicles per army in a single battle you'd better clear some time.

Man that was a fantastic game. I still have plenty of those minis, and probably will never part with them.

Good news: Though the scale of the plastic WotC minis is a bit off from the WEG ones, they are on 1" bases... which WEG's Star Wars Miniatures Battles requires. So if you used all WotC minis, everything would work just fine.

As others mention above, WotC Star Wars miniatures have been the core for our games (and my players hope to never see all the stormtroopers I own at one time LOL).

https://www.reapermini.com/Miniatures/chronoscope/

Reapers Chronoscope line has a lot of good sci-fi miniatures, and with several of them making their way over to the inexpensive 'Bones' line makes some of them super affordable.

https://www.fantasyflightgames.com/en/products/dust-premium-miniatures/

A lot of the miniatures from FFG's Dust also work real well.

http://www.wargamesfactory.com/webstore/dreamforge-games

I have several of these myself and I really like their attention to detail.

As for system, depends on whether you are looking for more small unit or larger scale battles.

Smaller scale, we enjoy Judge Dredd & Supersystem. Especially Supersystem. While it is a super hero mini/table top strategy, the system is SUPER flexible and I've made many different lists based on everything from fantasy to Star Wars with ease.

As for larger scale, of course 40K could be adapted, but....

Also, Bolt Action is an easy system and seems like it could be convertible. Never played Dust, but heard a lot of good things about it.

One of my favorites has always been Warlord from Reaper, it's fantasy based, but should be adaptable easily if you want to put the work into it, especially if you can find the first edition rules as they effectively have "make your own mini' rules. There is also a Sci-Fi battletech like version of it called CAV, though I never got the chance to play in this one.