Argo Sprocket question

[Mike T]

I'm replacing the front chains on my '93 argo. One was broken, and I noticed on the other side the chain is jumping on the sprocket when I roll the wheel. I hope its just due to the chain being stretched, but if not, is it a big deal to replace the sprockets? Are they secured on the shaft by just a bolt, or are they splined or keyed?

Also, do they only come from Argo or can you find replacements at other places? (Motion Industries is where I got my chain)

Thanks for any help!