2013 specialized allez race smartweld headset

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Hello everyone i currently own a 2013 specialized allez race smartweld that i had purchased second hand. My headset sounds a bit gritty and id like to replace the top and bottom bearings. do I have to replace the whole entire headset with the race? can I just replace the bearings? and if so where can i find them because i cannot find them anywhere. any input would be greatly appreciated.