They might be too tattered, but the Pig Iron Kolony line (the Ferals, and possibly some others) have some great options. A bit post-apoc in appearance, but they have clearly sci-fi rifles.
If you're willing to do weapon swaps, there's tons of great post apoc minis from EM4 (Grenadier Future Warriors), Copplestone, Lead Ad, Trollforged and many others that could useable with a laser rifle instead of a 20th century'ish firearms.