If it were me id just look on Craigslist or ebay for a cheap one that needs to be rebuilt that someone is selling and pull the parts off that i needed......if i couldnt find one that way i would look on Craigslist for shops offering carb rebuild services and call and ask if the had the parts theres all ways two or three shops in my area that offer carb rebuilding service,or id call local hotrod shops looking for the parts or a cheap carb...and last id just get on the phone with someone at edelbrock and order the parts but this will probably be more expensive then finding a used carb needing a rebuild...and another option is goto a carparts swap meet and find a used carb........edelbrock 600 cfm carbs are a dime a dozen shouldn't be hard to find a used one....
heres edelbrock's info off the website on how to get ahold of them:
http://www.edelbrock.com/automotive_.../contact.shtml