They've been available for a while, it's just that I only recently stumbled across them. Check out Exontrol I particularly noticed their Gantt controls. In one of our PowerBuilder based applications we were using a different third-party Gantt ActiveX. The original vendor left the market quite some time ago. We had purchased the C++ source code while they were still in business and had some some minor mods to it. However, we we decided to migrated the application to 64 bit we opted to do away with the Gantt functionality rather than trying to take on the task of converting the ActiveX to 64 bit. All of the controls shown on the Excontrol page come in both 32 and 64 versions, so that is not an issue with their controls.
The other thing I noticed is that they have a ExHelper tool that generates the syntax needed to interact the controls in a number of different languages, including PowerBuilder! One of the major pain points working with ActiveX controls in PowerBuilder is late binding and lack of autoscript, which leaves you just trying things recursively until something works.
Here's a video where they demo using one of their controls in PowerBuilder, including using the ExHelper tool to paste in PowerScript code.