I hope this will be useful, recently found on the net. It seems fairly comprehensive - includes both the old & new world mints. Mint die-sinkers and assayers My interest was trying to locate information on Seville assayer Melchor Damián - this coin in fact (dating c1550s-1566 Reyes Católicos 4 Reales) and it lists his start date as 1566 with the Felipe II coinage! Clearly not 100%, but its a useful concordance. Enjoy!
Thank you for the link! The two other references that I use for assayer information is Dan Sedwick's The Practical Book of Cobs for Spanish colonial mints and Krause;s Standard Catalog of World Coins - Spain, Portugal and the New World. The Sedwick Book is quite comprehensive for the colonial mints. Krause's lists are also useful but sometimes a little spotty, especially for the Spanish mints.