any major should have it - have you been lookin in the laundry products dept? that's what it's sold for - if you can't find washing soda, use baking soda - washing soda is sodium carbonate, baking soda is sodium bi-carbonate - same diff for the process, as either one acts as a 'water softener'
the process does work well, and using excess soda doesn't speed it up - make sure you dry the piece as fast as possible when it comes out - hair dryers are a good thing
I use sodium carbonate [50# bags from a chemical supplier, waaay cheaper
] in a big old bottle washing machine, and the inside of that 50 year old rig is as clean as new - handy for an old truck guy to have that stuff around!
