can you slow them down with gravity turrets? I forgot if they are immune to gravity effects or not. Do you have spire maws? They effectively eat the spawned blades. Otherwise make sure you have a bunch of ships that have a multiplier against it's hull on the planets you want to defend the most (and turrets). also build high mark Logistic command stations, they significantly decrease enemy speed, giving you more time to defend against them.
Hope this helps a bit. If it doesn't, I'll get back on this later today or tomorrow, since I'm dealing with blade spawners (and using them myself also) in my current game as well.