There were licensing problems with these (they needed Williams permission and in some cases 3rd party permission e.g. Star Trek) and never got released for sale "officially".

Having said that, a few selected apron titles did get sent out for evaluation, mostly to collectors in the US and some inevitably make their way to ebay from time to time.

Last MM apron I saw went for $400 US
http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&_trksid=p4340.l2557&item=220840189899&nma=true&rt=nc&si=mqlnmVjYH3j29wCM5X4ALUNRw9k%253D&orig_cvip=true&rt=nc

Pricey....