Are there any muscle relaxants that can be bought without a prescription?

None. Unfortunately, there are no muscle relaxants that are for over-the-counter use. If needed use OTC NSAIDs or Tylenol (acetaminophen) for pain and inflammation.
No. Unfortunately no, not that i'm aware of. Over the counter, your options for pain are tylenol, (acetaminophen) Ibuprofen (aka advil or motrin), and naprosyn (aka aleve). There are many topical over the counter treatments too, such as aspercreme and capsaicin cream. Good luck!