I have yet to see one. No doubt, somebody, somewhere put a front sway bar on, but if they did it was mounted below, or at least very near, the lower A arm and therefore is not seen in any pictures I have seen. Sometime ago, it seems that I recall speculation as to whether there ever was a front sway bar on a Mk I.
For what it's worth, I have heard the comment from more than one replica builder that testing showed imperceptible difference when a front sway was used vs when it was not. That said, I have fitted one, albeit pretty thin.