If you can find them online using the make and model number, you might for universal knobs that many appliance outlets sell. Even Amazon.
Here's some at Ace:
http://www.acehardware.com/product/index.jsp?productId=1279536
The are 4 , 5, or 6 Quarts. This is a little known brand called Royal from China. If you have one, just take a measuring jug, or a pint beer mug and add water. A 'quart' is 2 pints.
If you are thinking of buying one, run away!
https://www.google.com/search?q=Smart+Pot+SC22
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If timing does not allow the recipe to be cooked on low for as long as required, the slow cooker can be turned up to high and the cooking time reduced. Convert cooking time by using a ratio of 2 hours of cooking on low as being equal to 1 hour of cooking on high.
Try contacting CrockPot......
at 1-800-323-9519 or email at [email protected].
Monday to Friday from 9:00 am till 5:00 pm EST. Their product specialists will be more than happy to help you if the part is avalible.