RQ Net Asset Value -- daily historical

WRDS.
You can find daily and monthly data for closed end funds, within the CRSP Stock datasets. For example, Central Gold Trust, with permno 91439, cusip 15354610, or ticket GTU, you can find daily price, return, and volume data from September 2006 until the most recent CRSP update (for example: http://wrds-sol1.wharton.upenn.edu/output/grid/133407573.html?). You can use CRSP quarterly update queries for more timely data: http://wrds-web.wharton.upenn.edu/wrds/ds/crspq/dstk/dsf/index.cfm?navGroupHeader=Quarterly%20Update&navGroup=Daily%20Stocks.

Also on Bloomberg.