Vikki was correct - there´s a new repro hood latch out now, offered for '68-'70 Pontiac GTOs and '70-'81 Pontiac Firebirds and Trans Ams but the latch itself looks like fitting 68 and 69 Firebirds, too.
In contrast to the correct 67/68/69 hood latches there´s no pre-installed handle; you obviously can screw in whatever handle will fit:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=170202488045&ssPageName=MERC_VIC_ReBay_Pr4_PcY_BIN_IT&refitem=170200694210&itemcount=4&refwidgetloc=closed_view_item&usedrule1=CategoryProximity&refwidgettype=cross_promot_widget&_trksid=p284.m183&_trkparms=its%3DS%252BI

Not sure if it shows the same dimensions and if it really would fit a 68/69 Firebird hood but at $11.99 starting bid it should be worth a try...