I did not replace or use another heating element, I just recycled the broken one on the smoke unit and cut it into half length, resolder it back to the circuit board; so you may get the heating element from a broken solder iron and make the length with a resistance of about 5 ohms and that would be fine. The heating element was circularly wrapping around the white color cotton wick (or string, it is hard to see at the first place) and the diameter of the stock wick is too thick and heavy, so I just use a less diameter (about 1/3) from a regular gift-wrapping cotton string for replacement.

The wick shown on the right side has similar dia. as inside the smoke unit (actually it is a shoes lace), the one on the left I used for replacement. Wrap the heating element around the loop section of the wick, resolder back to the board. Done.

P.S. after months of fix, the smoke unit is still working.