Fuming might be the solution as marcros suggests. I've used box trailers and Luton body vans as fuming chambers for large stuff - it saves rigging up a tent with softwood and plastic, especially if you already have a vehicle you can utilise, or any other suitable chamber. .880 ammonia is what you're after and it's available from most polish retailers, e.g., Rydenor. After that it's just a case of putting some ammonia in a shallow dish and experimenting with exposure time to get the darkening you're after. Worth being aware of is that the oak, once fumed, will have a green tinge, but this disappears as soon as you apply a polish.
If you go with dye, e.g., walnut (Van ****) you might prefer an oil or spirit based version as these penetrate the open pores of oak better than water based stuff which tends to bridge across the open grain leaving the bottom of the furrows or pores undyed. You can help overcome this by adding two or three drops of washing up detergent per half litre of dye because this reduces the water's surface tension.
Lastly, best of all might be a pigment stain because the pigments lodge in the open pores of the wood which might go some way to replicating the grime that's already worked its way into the existing church furniture you're trying to match.
Dyes don't contain pigments, although it's hard to tell dye from stain here in the UK just from the label on the container because UK manufacturers typically use the words dye and stain interchangeably. If the instructions on the liquid's container tell you to stir the colourant regularly during application you're working with a (pigment) stain. Lack of such guidance indicates a dye.
As to a final finish, it's hard to say without seeing the originals, but if these are a century or more old they're most likely to have been finished with wax alone, or perhaps a sealing coat or two of lightly applied shellac followed by wax. They may even have been finished with boiled linseed oil and wax, although spirit varnish is a possibility. Whatever the base coat might have been, if any, I'd be somewhat surprised if wax wasn't part of the job somewhere down the line. You could do something similar, e.g., spray a light coat or shellac or lacquer just to seal the grain followed by a wax of some sort. Slainte.
