Source for GSN Batt Check lamp?

Hello desertratt , and welcome to the forum!

If you look at photo #31 in the repair manual posted on this forum, it shows one indicator light type used over the course of production. The one shown is the earlier variant. It uses a very small glass-encased filament, and commonly known as a 'wheat bulb'. These type of bulbs are still available new, like these, so as long as they match voltage/amperage specs, you should be able to find replacement parts and won't need to find a donor body to pull parts from.

A couple of things to note. The other possibility is that the bulb eventually became an LED as a logical, modern replacement, but that doesn't require that an LED has to be used. Both will work in the circuit, so you can choose to mix or match types. Lastly, the bulb/LED sizes and shapes may have changed over time, and I presume the bracket that holds them might also have changed slightly. Measuring for 'the pocket' in the bracket will insure the replacement part will physically match as well.