How would I best say
opportunity still knocks / todavía de la oportunidad golpes

Is golpes the right word for this?

That's a metaphor that might not work very well in Spanish directly translated.
You could say Hay una nueva oportunidad or Todavía hay oportunidad.

When I think of opportunity and golpear, I think of opportunity beating me over the head! Not good!

Felipe's are good:
Todavía hay una oprtunidad
Hay una nueva oportunidad.
Other options:
Todavía queda una oportunidad
Todavía te queda una ocasión
It's more lays than knocks, but we say it this way :D
The most nearly (but complicate)
Todavía hay una oportunidad golpeando a tu puerta. :D

gracias para todos

I did not like the way golpes sounded either. I didn't think that would be how the Español would say it.

What I ended up with instead was
todavía viene de la oportunidad / still comes of the opportunity

How does that sound?

It's easier to get an idea of the context if you can post a complete sentence, otherwise the translation might not be very good.

Another option might be:
La oportunidad todavía llama a tu puerta.

calls at the door does sound like it might be the way they might say this, but is there a native idomatic phrase for this. el preguntarse