Try John Saunders at Century Arms, he now sells traditional horn striker blocks for letting down the firing pins of doubles, rather than snap caps.

http://www.centuryarms.com.au/docs/hornstriker.html

Kynoch in the UK do 'em, but they ain't cheap - see their snap cap price list, downloadable from this webpage, http://dmt-hosting.co.uk/kynoch/shop.html