Automobile turn signal flashers were originally made to be load-depended so that if a bulb burned out, the other bulb and the indicator lamp on the instrument panel
blink -- alerting the driver that a bulb was out.
When people towed a trailer with these cars, they had to replace the flasher with a Heavy Duty flasher. A HD flasher is not load-dependent, so all six turn signal bulbs would flash normally.
Many Heavy Duty vehicles (trucks) came with HD flashers from the factory, since they were expected to pull trailers.
Buses are not expected to pull trailers, so it is reasonable that a bus could have a "passenger car" flasher, so the driver would immediately know if a bulb burned out.
If your vehicle has an old-fashioned non-HD flasher, simply pick up an HD flasher at any auto parts store.
In recent decades, more complicated flasher systems have appeared, and I know little about these.
However... I like to -- I insist on -- being able to hear my turn signal ticking, to avoid inadvertently driving with the turn signal on. For this purpose, I use a "honking big" commercial flasher that I first discovered in a Peterbilt. Then I recognized the same nice clear ticking in UPS delivery vans.
Mine are Dietz 10-53.
Pay attention to how you wire it. If I remember right, it draws current even when not in use (thru ground), so be sure the power to it is shut off when parked. To make it work with 4-way emergency flashers, I have a toggle switch that powers it even when the ignition is off.
Complicated, yes, but I love that crisp ticking that keeps me from driving half the day with a turn signal on.
With a HD flasher, LEDs work just fine.
However, LEDs tend to shine in one direction and are difficult to see from an angle.
Also, they do not last "forever". Individual diodes conk out regularly.