If they really are made from the tines of a farm rake or harrow, then they will be made from spring steel.
Your blacksmith will probably, unless you tell him (or her) different, will make it from mild steel.
Mild steel will have a duller tone with a lot less sustain. It will also be quieter.
The Cajun ones I have seen are up to half inch diameter- call it 12mm, and Engineers' suppliers will be able to supply Silver steel in that size. To make a decent sized one you would need a metre length. That would be springy enough to sound good, but it would need a Smith to bend it- and they would be only too happy to forge the curly ends.
Cheers
Dave