Do you still have the old one?
I would try to build my own pack. It looks like they were carbon-zinc. You could use three Alkaline or even nimh of whatever fit, and wire them in series. I can't find dimensions for them, but my guess is 3xAA.
The only sources I see are in the UK here. It looks like it may be a 3AAA size pack but I can't find the dimensions. Depending on how much runtime you want you could consider lithium ion power for it.
The 3R8 is listed as being 51 x 41 x 16 mm. You should be able to fit a 3X AAA battery holder box in that space and wire it to the light's contacts setting it up to run on 3 AAA's.
I have the old ones and want to revive.I consider them very good flashlights in terms of durability and simplicity (no circuits, no leds ). their bulbs can be found easily and regarding battery probably a DIY pack is the option