First, you'll have to get the model/spec numbers off your engine. If it has the OEM Briggs in it, go to Briggs & Stratton parts. and enter your engines model/spec numbers. It should bring up an exploded view of your engine showing various function groups. Find the one for the carb. and open. It should have an exploded view of parts, and part numbers associated with it. Copy, and pate the part number for the carb. kit to a search engine. I have the best results using Google. You should get a ton of hits, from OEM vendors, to after market one's. Ebay is also a good source for NOS OEM parts. Just have to compare prices.
I just got an OEM carb kit for my 60's vintage Kohler K181 on Ebay a couple weeks ago for half, + free shipping what a local dealer wanted for one.