A retail outlet store that sells air conditioners is the place to go to buy air conditioner knobs. Stores such as Sears, Kmart, Target and other such retailers are most likely to carry replacement knobs and controllers for your air conditioner. You may also try a vacuum and small appliance repair shop or to a home improvement center to obtain air conditioner knobs.
Request Information from the Manufacturer
The manufacturer of the air conditioner that you own should also be a source to contact to locate knobs. The manufacturer can provide you with a list of recommended retailers in your area that can provide you with knobs, based on your location or zip code. The manufacturer should also have a facility such as a service center that can ship replacement knobs to you for your air conditioner.
If the manufacturer of the air conditioner that you own is out of business or no longer dealing with retail consumers, you may try placing an ad on sites such as Craigslist to locate air conditioner knobs. This may put you in touch with a salvage yard or owner of a similar model air conditioner that is not in use but has the knobs that you are looking for.