I don't know how pure it is. Several razor places are sold out of it right now, including Fendrihan.
I bought mine on Amazon. https://www.amazon.com/gp/product/B079S3G7WY/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1&p ldnSite=1

I used green, not the white. The green is supposedly .5u. Honestly, I doubt its purity, but as a nice cheap test it worked out OK. The balsa I used was 1/16" thick, and is 12"x4" with several pieces in a package. Placed on a solid table for stropping.

I also bought Herold Solingen Stagenpaste Solid Double Paste for Razor Strops, red and black paste, but it has not arrived yet. This appears to be a foil-wrapped bar instead of a cream in a jar.

If you have a better supplier in mind, I'd love to know where to buy.

I used balsa as my cheap test. So far, results are good! Euclid, I believe one of your posts from a long time ago showed your fabric strops, and I like your setup. Some D-rings are easy to buy, and if you could let me know where you bought the fabric, I'd appreciate it. If you need to send a PM that's fine.

Based on my paste test, and as basic and rudimentary as it admittedly was, I'd like more info on where to buy pure Chrome Oxide and fabric for strops.

My paste test was good. If higher quality or more pure paste is available, and I apply to a better medium like cloth strops, the results may be even better. I'm willing to jump in. Love some details as mentioned above.