Spikehelmets.pl has a decent selection of repro parts, the prices aren't terrible if you buy from their website or FB page. They're not perfect, but just looking at their site now I see they only list 70mm, but I noticed they have some stuff on their eBay page they don't have on their site so it's worth asking.
I do not recommend the cheap $20 ones from spike helmet Berlin unless your desperate, they look terrible and are paper thin. The edges are too jagged and make the helmet look bad. However they do have some ok random parts and occasionally some decent cockades.
If you look through picclick.de or or directly through ebay.de it will show you parts from the German eBay sellers that you won't even see on the US version, including all the parts from spikehelmet Berlin that don't appear on her US page. I always reach out to confirm shipping to the US first.
Hope this helps
Edit: I saw your thread, the 1915 kürassierhelm also came with the smaller cockades if that's what your considering replacing. See the Kaiser's bunker article.