The correct M122 tripod rarely makes it to the market. The Army is still using them on the M60 an M240G. Most of the ones you'll see are surplus European ones that have been modified to fit.
Sold a tripod from our range's 1919A4 at Knob Creek last fall for $350, including T&E. I believe it was an M2 tripod, IIRC
You might try Ohio Ordnance Works www.ohioordnanceworks.com or the Lomonts www.klomont.com.
Someone from Ohio Ordnance told me that they had a warehouse full of M2s when I was selling ours.
