Hi Calvin 48,
The hot air balloon you were talking about is Thai Lantern or Sky Lantern (Kom-loy). In the past, the sly Lantern will be used or only Thai Lantern Festival. But nowaday, we use sky lanterns for all celebrations and other special occasions.
I saw many posts about seeling this Sky Lantern but all of them posted in Thai. http://www.pantipmarket.com/view.php?id=SV4349461
Let me know if there is anything I can help.