Over years I have had a couple that I could not move, not penetrating oil soaking for weeks, not impact wrench (although I think mine is wimpy), not big punches, and not wrenches with pipes. I realize everyone below is trying to not use heat. If all that fails I would suggest you torch the gear out and heat the crap out of the bolt/axle from both ends and the center. Then let it cool a day or two and then punch it out.
I have had a similar issue with wedge bolts between the rim and cast center. Believe me, I did it all. The only way I could get them out was to grind the bolt flush with the casting on both sides, heat the bolt cherry red from both sides, let cool for a couple days, then punch out. I did not have to do this on all but if you have a couple that don't respond this works. I was told at the time I was experiencing "Rust Welding".
Oh, if you do have to torch the gear and bolt, the new gear and bolt are an interference fit. Heat the gear and be prepared to quickly thread the bolt through the casting and the heated gear in its position in the casting. It works good.