Unfortunately for me, I have been looking amongst the most obvious suppliers of HART equipment, including the two suppliers already mentioned but while there are several manufacturers of HART to 4-20mA (aka Tri-Loop contraptions) the best that I have been able to identify for the reverse, ie 4-20mA to HART, is crude adaptions of HART temperature transmitters. You see, according to my way of thinking I expected to find a universal HART 2-wire thingy that takes in 4-20mA and is programmable and configurable by me to respond as a new HART device.