is there a list of android devices and their heap size?
Not that I am aware of.
Could I simply assume that all devices with 512MB Ram have 32M of heap?
Heap size recommendations are driven more by Android OS release and screen size. Android OS release and screen size also have an impact on minimum effective RAM on the device. So the concepts are loosely correlated, but that's it.
I'd like a list so I could determine mainly if Android 2.2+ devices with 16mb heap exist
AFAIK, you cannot rule out that combination. After all, please remember that Android is open source, so modded ROMs are welcome to configure heap sizes however they want. IIRC, at least one allows the user to choose the heap size. And there are no rules regarding device RAM or heap size in the Compatibility Definition Document, so device manufacturers are welcome to try odd combinations.