How are you at writing code? That's the only approach I see.
I'd find the first ( using Instr function, then find ) and then use Mid with the starting point being the first value and the number of characters to take being the difference between the two. Then I'd test the result to see whether or not it can be interpreted as a number, in which case it will not be if it looks like "123?"
Then you could write the value to a table.
Alternatively, one could loop over the first value until the second and test if it's a number but I don't think that's the approach I would use.
EDIT - seems I misunderstood the requirement as I thought that (123) in the middle would be needed as well.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.