A research of Aqua history might help you in your problem. Go to this page of my website: http://petrolianacollectibles.com/pc-1.htm
Click on Company Histories
Scroll down to Aqua, you will see that Aqua became a part of the Neptune about the time your pump was made.
If you have a copy of my Gas Pump ID book, look up the Neptune 855 pump, I believe your pump is identical to the Neptune 855, and now you have two places to look for replacement parts.

Jack Sim

Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at www.gaspumpbible.com
Air Meter ID book also available