While doing a subtractive boolean mesh set I baked these alphas as a by-product. 51 alphas 16-bit TIF in total.
https://gumroad.com/tenitsky#MOkiw
They are of high quality in a range of 1-2k pixels each. Use it for anything you want - commercial or non-commercial. Just don't resell or redistribute. No credit required. Stay tuned for the mesh set.