Where are you located magichat?
You may be able to go to your local hardware store and get a NEMA 6-50 0receptacle, and whichever dryer plug you need, along with a length of 8 0r 10 awg cable (possibly a short drop from the "Scrap" bin for a significant discount) and make up your owm adapter. If you do go this route, I would consider getting something with some length if it is appropriate for your welding location.
John
Everlast 200DX
Everlast PT185
Shoptask 3-in-1 (not currently in my garage, but I own it...)
Any day on a motorcycle like this that ends just needing parts and labor is a good day.
4.82, 158.67mph 1/8th mile 7.350, 200.35mph 1/4 mile