I've had to fight with them myself. Sliding off the keyway is the problem. Here is a consideration you might try. Look at your cam/gears to see if this might work.
Put the bolt back into the cam to protect the threads. You will need 2 chisels or big screw drivers that you can wedge between the cam gear and block, something you can tap in to put some pressure on them - not killer pressure, just a reasonable amount (never heard of a block cracking from this, but just be careful). Then I would find a big socket that will go over the cam bolt and be large enough in diameter to still fit within the inside diameter of the cam gear.
With some pressure being applied to the cam gear on each side from your "wedge" you tapped in, give a couple good solid hits to the socket. You are trying to "shock" the gear loose off the keyway using the wedge to force it forward while hitting the cam to force it backward. After a couple good hits, if it still does not move, tap the "wedges" in a little tighter. Hit the socket again with some good hits. I would also hit the cam gear a few good times on the teeth edge where the wedges are not at. This may rock the gear just enough while they are on the "wedges."
If no luck, move the "wedges" 90 degrees to another location (or turn the cam 90 degrees) and repeat. Sometimes you have to rotate your "wedges" at different points on the gear to get it loose by applying pressure at other points on the gear. Repeat above.
If you put an uneven pressure on one side of the cam gear or the other, you will be tilting the gear and this will only make it more difficult for the gear to pop off. So it is always best to use identical type "wedges" to give you an idea that you are getting the same kind of even pressure.
You might even consider a little heat from a propane torch by applying heat around the gear just outside of the camshaft while you have your wedges inserted. You want to keep the camshaft cool and heat in a circular motion the metal adjacent to the cam. You are trying to expand the metal just a hair. Then give the camshaft a pop to break it loose from the gear.
A puller should work -although I have never used one on a cam gear, just a lot of prying. Have you tried your local auto store to see if they may have a puller that would work? My parts store has free loaner tools that you simply put a deposit on and get refunded once you return the tool. You might find one large enough to grab the outside of the gear.