Honestly? Anything that fits and pushes the takedown bar up. That takedown bar just needs to be in the way of a lug on the barrel during assembly; the spring has no other job than to ensure that.

I heard bic lighter springs work as well

I tried some springs I was linked to on Amazon (forgot from where) and buyers mentioned they worked on Pews, so I bought them. Well they fit in ok, and I got the slide on ok, but holy shit it was a bear to get the slide off! These springs had a few too many coils and were slightly thicker wire than OEM springs, so they wouldn’t compress enough. I bought some Glock springs and they work MUCH better! I’ll pull some out and take a pic for you.

Glock spring on the LEFT Amazon Spring on the RIGHT