Hi John,
National Instruments still ships AT-MIO-16X boards. One such board can be seen at: http://sine.ni.com/nips/cds/view/p/lang/en/nid/1045 .
The following is the result of a product search for AT-MIO: http://search.ni.com/nisearch/nisearchservlet?nistype=default&ddown=7&filter=%2Btaxonomy:%22Products+And+Services%22+%2B(language:en+nilanguage:english)&cluster=false&q=at-mio .
You can order these boards online or place a call to an ISR at (800) IEEE 488 (433-3488).
I hope this helps.
Regards,
Sean C.