Usually these circuits have a coil to generate a large voltage using an oscillator circuit, this voltage is across the two ends of the glass tube. There is a trigger wire on the glass between the two ends. This is what makes the tube light when it is driven with another high voltage. If we can identify the "bad" component it should be an easy fix. Caution that high voltage can hurt!
Alternately a surplus camera flash can be substituted, but this would be involved because you would need to wire it in to trigger off the MFU. I did a project a while back and I believe there was a Heng Long flash unit available that I used for an 88 gun flash. It was an easy hookup if I recall correctly. That may be another option.