WTB 6"-7.5" OD pipe - Aprox 1/2" wall

[opsoff1]

Looking for a 4-5" long section of pipe - probably DOM, not sure of the alloy - but looking to weld it to A36.
I am (attempting to) fabricate a column riser for a Clausing 8520 series mill. Trying to duplicate the riser made by Joeuser01 in this thread; Riser Block

TIA