We are close to completion of a Braintree implementation if that will work for you. The process of creating a new payment gateway is more involved than I would like. It takes us two solid weeks to get a new "official" Payment gateway into the framework. You can take some shortcuts if you just need a single function (e.g. if you are not planning to handle refunds / credits / void /etc.).
For now, we've started documentation which can give you insight into the process:
http://wiki.broadleafcommerce.org/displ ... t+SolutionWe are working to make adding and using payment gateways simpler but honestly, we are a 3-6 weeks away from being able to spend any quality time on this.
We greatly appreciate contributions in this area and will work with you to get something as an officially supported addition to the framework.
Thanks,
- Brian