Oak mouldings

Do you have a router?

Probably won't match. Assuming this is an old clock, those mouldings were cut on a wooden-bodied hand moulding plane. Mouldings cut on a router are ugly in comparison, from the limits of the tooling. You have trouble getting sharp arrises (ridges), you certainly can't cut a decent vee groove with a router.

Your best option is a wooden moulding plane. Many of them will match, surprisingly well - many of the shapes were standards, even if you need two planes in two passes to cut a complex moulding.

The practical option though is a scratch stock (JFGI). You make this yourself, matching the profile in a piece of steel (old sawblade) and then using a commercial (Stanley #66) or home made wooden holder.

Custom sized cove can be made on a table saw...

Radial arm saws work well, too, with easy control of arm angle and blade

-to-table height. I start with a length of oak board, say an inch or so thick, form the concave moulding first, then rip both sides of the moulding to a 45 degree chamfer. It's much easier to work with a flat-backed moulding than one which started out as a square section, uses less timber, and is almost certainly how the clock would have been made originally.

Yes, but not a 1/2" one and a cutter large enough for this coving would need to be 1/2" and they look quite pricey:

Yeeeees... I've seen some howtos on doing that. It's my fallback at the moment if I can't just buy some. I have enough work to do with the clock I'm making without doing that.

At some point I'm probably also going to want to get something along the lines of this:

Jon

Cove bits are like:

I've seen this type of cove/scotia moulding ex 50mm softwood. Wasn't that the size the OP was after? Too big for a router I reckon.

Short of sourcing one (which has proven very difficult), it does look like the best option.

Jon