Wien bridge oscillator - what is a suitable replacement for the "bulb" typically denoted?
I believe you might benefit from Linear's Application Note 43f. Look for the section on Wien bridge oscillators. Jim Williams tried replacing the bulb with JFETs as well as a photocell "vactrol". Essentially, anything that has a nice linear transconductance would be a good candidate.

If anything, the app note is an excellent read and Jim Williams was a rock star :-)