There aren't too many side-kicks in this sport period. It's the Muay Thai influence; side-kicks are a lot rarer in Muay Thai than they are in Taekwondo or Karaté or Wushu or most other non-SEA kickboxing styles (Muay Thai, Lethwei, Kun Khmer, et cetera), and a lot of Muay Thai places kind of discourage the side-kick. That's a good part because of the Muay Thai ruleset and the emphasis on certain aspects of the style that end up favoring the roundhouse kick above everything else, but still, the point is that, considering the influence of Muay Thai on this sport's striking, it makes sense why there're so few side-kicks, so there'd obviously be less flying side-kicks.
Zheng Yuhao and Eduard Folayang throw a lot of jumping side-kicks in their fights. They're off their lead-leg and they're not really flying-- they just jump forward when they do the kick sometimes-- but it's still a close example. I think Cung Le also threw 'em a few times.
In terms of flying kicks in general, Dejdamrong Sor Amnuaysirichoke throws them a lot. They were his weapon of choice against Roy Doliguez last year.