Just about all coin op parts distributors carry these as they are a
common bulb.

Amusements Plus in Rochester, NY (1-800-377-7729 or 585-244-2420)

Happ Controls

Betson

Competitive Products

Pinball Life I think has 'em too

Even your local NAPA auto parts stores carry them. I know cause I
bought some there for a Rowe CD100 that was on location way out in the
sticks.