Hi I’m new to the forums, and for some reason my search function is not working, I’ve got a 1973 ct3 and looking for some insight on a 42t rear sprocket, I’m aware I could get a 16t front and be almost the exact same ratio, but would rather replace the rear as it’s been changed before to a 47 or so, are there any other sprockets from other bikes available in a 42t that will fit? Just looking to make a nice cruiser out of it since I’ve made it too nice to talk myself into dirt biking it anymore   

Be sure you use the "search forum" and not the "search".  Not sure why the plain "search" is here but that's likely the problem.

Tons of sprockets available.  If you want aluminum you have get one any tooth count you want.  You need to get one with the relief on the back side. 

69-76 AT, CT, DT125, DT175 are the same.  Using the search you can find the "industry number" and names of several manufacturers of aluminum sprockets.  Otherwise, search ebay and see if you can find one.

Welcome from NZ down under. Man that's a nice looking bike so i won't show my ratbike 175. I have a 37 on the rear on mine & a big one on the front. Is a TY175 cylinder & AG175 farm bike head--just a CT3 head really--on an AT1-125 bottom. Tis geared high for sure but pulls it good & original 125 pipe livens it up about as opposite to a trials riding TY as you could get. Magneto AT1 that is, not electric start like in the US.--I'm in NZ.