Recently hot air balloons and numismatics were mentioned together in The E-Sylum. There is a gem of a little book (96 pages) about the topic, called   Lighter Than Air, 200 years of Ballooning in Numismatics, by Evelyn Malpas.

The book was published by the British Art Medal Society in 1989 and catalogs 461 numismatic items – mostly medals but a few awards and plaques and the like – depicting balloons. A quick check of the American Numismatic Association library catalog confirms that it is available for loan to ANA members. Cheers!