Not an experienced 2 cycle guy so, on that note, how is it seized?
Did you take the plug out and see if the cylinder is full of fuel? If it is indeed stuck, transmission fluid, marvel mystery oil, PB blaster have been known to unstick a piston. Just pour it in the spark plug hole and tilt the mower back so it will cover the top of the piston and let it sit for a few days. Walk by every once in a while and give it a little pull and see if it has loosened up.
Someone else may know a better trick, if so, I'm all ears!
I got one of these a few months ago. It was also seized, but the price was right (free). I swear all I had to do was tug the blade a bit with my bare hand and that was all it took. It runs great. I've no idea why it was seized. I've gone through a couple tanks of mix since. My only problem is with the throttle. It doesn't like to go into the choke position without some effort. I've been meaning to take a look into that.