Found a correct and rebuildable Carter AVS 4618 for my '69 HP 440 A/T but I'm not naving much luck finding the right fitting that will connect it to a repro 3/8" fuel line. Any suggestions?

Edelbrock fitting adapter inverted flair part# 8090 from Summit, Jeggs or anyone that sells Edelbrock parts.

It is not identical but it fits & should do the trick, like the Carter fitting the Edelbrock one has a 3/4" hex although it is a bit (.177") longer, brass rather than steel (different colour) & is not counter bored for the factory style mesh filter although this could be easily done with a standard drill in a lathe or drillpress if required.

At least it would get you going until you found an original one.

Here's part of your problem , the repop line is NOT 3/8" , it's 5/16" , the Ebrock piece that is available is for a 3/8" line .

Now there might be a repop available , it's made for HEMI carbs ???

Try Walkers

http://www.walkerproducts.com/_pdf/carter4barrel.pdf

scroll down to pg 67, they have the thread sizes stated for you to compare against yours.