[hiredhand]

Oxalic acid?

...never heard of it! Where does one obtain the stuff?

[DuncanWaring]

You might find it at a woodworking/finishing supply place, or possibly a large pharmacy.

Or, you could try these guys:

http://www.cheap-chemicals.com/filter.asp?f=CH8205&m=1&cm_guid=1-_-100000000000000000620-_-730938623&cm_mmc=Google+AdWords-_-Chemicals+-+Oxalic_Acid-_-oxalic+-+Phrase-_-+—+730938623|-|100000000000000000620&gclid=CPC5rMzXy5kCFQoMDQodm2pmuA