Leaf Spring u bolt nut problem !!!

Hi
Im trying to remove my leaf springs and then the axle so I can get it powdercoated.
The ubolts are sort of rusty , I shot some lube on there to soften em up but it doesnt seem to be working. Are the nuts that I am trying to take off supposed to be difficult to remove, like oval or something. An impact gun wouldnt take em off, I had to loosen them by hand with a pipe breaker bar adapter on my 1/2 ratchet. I gave up for the evening before getting them all the way off.
If they are too rusted to reuse where is a good source to get some new ones ?
thanks