Hi Dirk;
FWIW: I love IM too and use it every week (SAP InfoMaker – SAP Help Portal Page)! 
IM is still included with PowerBuilder when you purchase the IDE. IM is also still available commercially and can be purchased through many resellers, for example:
TechXtend:
Kernel Software:
USA - SYBASE Price List as of 4 Jan 2016
Novalys:
I think IM is also available from this world wide reseller of PB (Get PowerBuilder).
IM is a subset of PowerBuilder. As such, it is my understanding that this product will be included in the deal that SAP is making with Appeon Corporation to handover all PB & related technologies for future development. What we do not know at this point is what Appeon is planning to do with IM. Appeon is currently busy planning their PB Road-Map and is also looking for feedback on what the PB Community wants in a new PB product. I would suggest that you also contact Appeon and ask them about IM (Vote for Feature Requests)
If you decide to move away from PowerBuilder though, you might want to have a look at the new Reporting Studio. RS is written in PB Classic and uses Appeon technology as well to run as a Web, Android or Apple application as well as standard MS-Windows native. RS is available through Novalys at: Reporting Studio
HTH
Regards ... Chris