Maybe I'm thinking in terms of 'guitar callus', but I figure that in cardistry, you just get better feel for how to perform a flourish.
When I first started, I was gorilla-gripping the deck and hurt my hands when doing flourishes frequently. But after doing the same flourish over and over and over again, I started getting used to it and eased up a bit. For you, maybe even adjusting your grip ever so slightly to a position to where you get the same results, maybe hurt yourself less.
While I am not familiar with card springs at all (it's a two-handed flourish. Not what I do), all I can say is to keep practicing. I know you're new and plowing through as much as you can. Just keep going.
I will say that I've managed to create a variant (it's a full packet 'Rinzler') that I can only do about 20-25 times continuously, as it seriously cuts up the side of my pointer finger just getting the packet into position. I haven't tried it lately (mostly because I'm very wary of doing so), but I think it all depends on the flourish you're actually doing, your grip, your deck, and your experience.
ALL of which requires a bit of troubleshooting on your end. The better you can troubleshoot a flourish your're having problems with, the faster you'll be able to nail the mechanics down.