Super confused about buying headsets

[HSK2133]

I have an Avanti Hotdog (might be 2002 model). The handlebar wiggles a lot and i believe there is something wrong with the headset. I bought it second hand the the guy i bought from took apart the headset (after i told him about the wiggle which he said he never noticed before) dropping them several times. I think some pieces are missing or broken. So I am looking for a new headset and the local bike shop ot even Avanti shop said they don't have what I need. I have cane creek Fatty mx headset. Am I only able to swap it out with that or are there an equivalent headset that is more readily available that I can replace with? I'm a bike novice and i tried my best on Google. I thought just any 1 1/8 threadless would be fine..

Any comments welcome.

Thank you

[Uncle Just]

This may assist...https://blue.canecreek.com/headset-fit-finder

[Ross]

This recent article from Cycling tips may be of help as well

https://cyclingtips.com/2018/05/how-to- ... e-build-2/

[Ross]

Also http://hub.this link is broken//buy ... ing-guide/