Check out this Amazon page:
https://www.amazon.com/125cc-engine/s?k=125cc+engine
Scroll down to find 140cc and 150cc motors. Might be easiest to buy a whole motor, and sell your 125cc one to someone who needs one.
Plan B: Big bore kits from Amazon.
https://www.amazon.com/s?k=125cc+eng...f=nb_sb_noss_1
Whichever way you go, make sure the product is in stock here in the US or wherever you are, not shipped from China when it is ordered. We all know how shipping is these days.
Also you will have to do the research to find out what big bore kit or whole motor will work for you. Good luck.