I found a source for kits, including accelerator pumps, for the Rochesters. They also supply kits for Carter and Stromberg carbs.
http://www.thecarburetorshop.com/
I bought one and it performs great! I also found out that two different Rochester numbers were used in 1958: 7011600 uses kit #1140, 7013100 uses kit #1141. You MUST have the carb tag number to order from this place - every year Rochester tweaked the carbs so the kit for each year and carb model number is different. If your carb tag is missing, the number is usually stamped onto the air horn (top of carb) - you have to look closely and make sure the top is clean to see the number.
This shop has all of the blue prints for carbs from pre-war to 1970s. Each kit is custom-made for your carb number. There were no extra parts in my kit, only what I needed. The accelerator pump had the correct leather plunger instead of rubber. It cost me about $60.00 - including shipping. When dealing with old original carbs, keep in mind that some are just plain worn out and rebuilding them will not fix them.