I too have the TB signals, but feel they are bright enough IMHO.
Anyway here are some suggestions you could try:
- use an LED bulb in the signals
- try a different brand of singal, like the previously mentioned RIZOMA singals
- add in some additional/extra singal lighting
Since you feel they are too dim in the day, then I would stay away from the all in one, integrated tail and singal units like the one from Clear Alternatives.