"Dime-a-dozen" is an idiom commonly used to describe something that is very common or easily available. There are a number of synonyms that can be used in place of this phrase. Some options include "ubiquitous," "widespread," "prolific," "commonplace," and "ordinary." These terms all convey the message that the item or idea being referred to is not particularly rare or valuable. Other possible synonyms for "dime-a-dozen" might include "run-of-the-mill," "garden variety," or "ten-a-penny," depending on the context and the specific meaning that the speaker or writer is trying to convey.