A source that I've used for rough service light bulbs is the local city
garage.  I used to get old traffic signals for the cost of hauling them
away.  Some I converted to flashing lights that people could use for
yard sales and other places to attract attention.  That sort of use
didn't require the rough duty light bulbs so I would sometimes save one
of them for use where rough service was a factor.

Try the local city garage or traffic garage and ask for traffic light
bulbs.

Hal