While there is no topical Botox product available at this time, it is currently being studied.
Many medications can be delivered through the skin, but the trick is to get them to actually penetrate and work below the skin. This is the difficult part, and the reason most topically applied versions of injectable medications don't achieve the same results (think topically applied hyaluronic acid... it doesn't really help wrinkles).
Topical Botox is showing promise, at least according to our colleagues who are studying it. But it's not yet approved, and may not be for years. For now, injections are your best bet