Hi, You found a great pump! The National A1 in my opinion is one of the best looking pumps ever made! They were manufactured here in Dayton Ohio. I have an all original A1 on display at the Benkin & Co. Nostalgia Store located in Tipp City Ohio (just 10 miles north of Dayton).
The parts are available from Time Passages, Vic's Place, Past Gas, and more. You can find there contact info on this website.
There are several ad glass panels that are reproduced for this pump. The one panel I need is not reproduced. It is a Texaco Fire Chief with Ethyl (Yes, I am still looking for one!).
If you are looking for original parts I would recommend attending the "Ohio gas 2001" petroleum show. This show is held in Dayton Ohio, and because it was the home of National each year there are several pumps and parts that show up. This year the show is held in conjunction with the "International Antique Advertising & Coin-Op Show". Both shows are held on May 4 & 5 in Dayton Ohio at the U.S. Air & Trade Show Building. The hours are Fri. from 4pm to 7pm and Sat. from 8am to 3pm. There is no early admission, and there are no sales until the public is allowed in at 4pm.
Good luck!