Where To Buy: Calcium Phosphate

Best for 8 oz to 1 lb containers of "Tribasic" or "Dibasic" powder.

with an acid (like vinegar) to create a calcium solution, or react with phosphoric acid to specifically yield calcium phosphate.

Recommended for bulk lab purchases (1 kg+). Industrial/Bulk:

If you specifically want , you are likely working on specialized "Inorganic Paper" :

Hydroxyapatite (a form of calcium phosphate) nanowires are used to create paper that does not burn .

Good for finding ACS (high purity) grade powder in small quantities from chemical resellers. Scientific & Research Grade:

Used for bone-grafting "paper" or scaffolds due to its biocompatibility.

In traditional DIY papermaking, people almost always use (limestone) to: Buffer the paper (make it acid-free/archival). Whiten the sheet and increase opacity. Retard shrinkage in paper castings.