Depending on how much work you want to go through; do a search for "tritium keychain".
Different-sized "vials" and different colors to choose from.
LEDs are getting smaller and smaller too. Especially with the 'surface-mount' versions. Making a new holder might be a job. But as a replacement for a standard filament bulb, adapting might not be such a big deal.
Miracle Machine Works
"If it's a good part-- it's a MIRACLE".