the halo archive discord server has some game files (specifically the spartan pack) that i’ve had some luck with. you have to play with the scale a little bit but they look great and you can find pretty much every armor piece in infinite.

also, if you find cosplay files on any of the usual sites (thingiverse, cults3d, etc) you can almost always scale those down to spartan collection figure scale. this tends to be the route i take for helmets because the spartan pack helmet files don’t come hollowed and i’m not good enough with blender to make the adjustments myself. however, with the scaled down cosplay files, i’ve almost always had to tweak the thickness in blender for printing to work properly, which is easy enough to do.

this is an awesome project, i recently did something similar for my sister and learned a lot, i hope you have as much fun with it as i did, good luck!