Ok, so here's a thought.
The reason turrets kinda suck is because you need to improvise them, right?
And colonists can't use charge lances, presumably because of either weight or electric requirements, right?
How about a high-research turret that simply is a mounted charge lance?
which would also outrange sniper rifles, I think, and have the same range as charge lances so you don't need to charge scythers anymore. I second this, but it should need some serious research.
Charge lance is mechanoid technology and one of the few items that can't be manufactured. Maybe as loot from ancient danger rooms ?
As loot from actual mechanoids themselves, Rsuk. Have them drop Unpowered Charge Lances.
don't just make them drop them, add a crafting recipe at the machining table that turns one scyther into an unpowered charge lance, which would require a crafting skill of at least 15 or so, and a special research project.