The later model carbs use "M" series metering rods (single main airbleed models). They are still available from Edelbrock, we don't sell them here.
The earlier carbs with 4 MAB's used "K", "L", or "P" series metering rods, non of which are still being produced or available commercially that I know of.
Ours are a copy of the "L" series metering rods, .044" at the upper section, tapering all the way down to .026" tips......Cliff