So an 18 165 just needs the 19 top gear. Those should be readily available.
Ace
Did a little research and found some info to share.
154" track has 21T 51T
165 has 21 -53
There are lots of 53 gears out there. It was a BRP fix for belt issues on a 154 factory belt failure in 2017 ;as told by a dealer.
19T called several places NOT in Stock.
Retail dealer is over a $100 Local shops are around $80 and direct manufacturers are around $40