Daiso had both alkaline and traditional carbon-zinc batteries in this size. I chose the latter because it’s for a 1960s device and I think that was the default battery chemistry in the era, plus modern alkaline batteries seem very prone to leaking when left alone for 10 years.
They sell (on Amazon) adapters that take AA batteries. Got a pack of like 8 for $10. Now I just need to have AA batteries + the adapters for the rare occasion that I need any D batteries.