First, welcome to OCC....
Next, the model of your Kohler Engine is M-18S not 5. Easy to mistake.
The Carb
53-853-24 (Walbro Carb) is No longer Available from Kohler.
The Carb Rebuild kit is. It is kit number
25-757-11S (or Stens 520-350).
The kit can be had from your local Cub Cadet, Kohler, or Case-IH dealers. The sponsors listed at the top of the page can also get it for you. And as always, numerous places "on line".