If anyone needs to know how I ended up figuring this out.

I downloaded the annotation CSV files from here (these files have hg19 coords), and joined the rs IDs against a dbSNP VCF:

http://www.affymetrix.com/catalog/131459/AFFY/Mapping+500K+Array+Set#1_3

As one of several solutions, I suspect, the UCSC genome browser has these data in a table snpArrayAffy6 but for hg19/GRCh37. Grab the data in bed format from the table browser and then use the UCSC liftover tool to move to hg38.