For those who can not easily go to USA, you may have had to get oxalic acid
from a pharmacy, quite overpriced. 
It does not seem to be available in building supply stores

https://www.ebay.ca/itm/oxalic-acid-1000-gr-1-Kg-2-20-lb-HOOC-COOH-2H2O-CAS-6153-56-6-free-shipping/153134359609?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

1 kg for $21.60

For all your wood bleaching needs !!

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