or contact the dealer / Rep. in your area.
The equipment I bout from them was always the right answer.
Mescon is good choice as well.
They are doing good instruments and the price is nice. Smar range is wider and more suphisticated.
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.