You can buy rebuilt carbs from several sources.
Here's a good one.
https://www.smicarburetor.com/
Or keep it in the same country and contact this guy in Vancouver area.
http://www.thecarburetorguy.com/
I've had quadrajets from both of them.
If you want to tackle a rebuild then let us know. I've got links out the wahzoo For that! LOL!!