There are a few synonyms that can be used in place of the word "buckwheater". A possible alternative could be "buckwheat farmer" or "buckwheat grower". Another option might be "buckwheat producer". If the focus is on the processing of buckwheat, terms like "buckwheat miller", "buckwheat processor", or "buckwheat manufacturer" could be used. Additionally, the general term "farmer" could be used if the context is clear that the individual in question primarily grows buckwheat. It is important to consider the intended meaning and context when selecting the appropriate synonym.