Here is a link to useful FIR engine chip:
They offer a DIP version for experimentation:
Mouser stocks the parts.
The current status is that I am working on integrating the QF1D512 part into the QS1R receiver prototype. I have no new projected availability for QS1R. In fact it appears that interest may be somewhat limited - enough so that it would not be worthwhile to offer assembled units. In that case the design files will be posted from anyone who wants to build a board.