I suspect the main problem is that there are few NOS condition Shimano hubs still around from that time period, and that few people take the time to unlace a used hub from a wheel when the rim goes bad (unlike say a Campagnolo hub may be resuced from a dead rim for a rebuild). I scored a set of used Shimano high flange hubs off eBay some time ago that I built up into a new wheelset to go with a Shimano 105 Golden Arrow group set that I had at the time.

What spacing are you looking for? 126mm? Or 120mm with a 6sp Ultra freewheel?

Here's a NOS Dura-Ace set in 126mm: http://cgi.ebay.com/Shimano-Dura-Ace...3A1%7C294%3A50

mod note: moved thread to C&V where it should get more responses.