[arcticap]

I doubt that drilling & tapping a barrel is factory authorized work at all.
I think that they will basically only perform repairs that maintain original or factory authorized specifications.
Contact TC if you must, but I think that kind of work needs to be done by a private party.
Any gunsmith can do it and you can find some online or in the Yellow Pages that are right in your own state.
Discuss it with them on the phone and then send them the barrel if you trust them.
But the scope will need to be mounted high to not interfere with the hammer, or the hammer will need an angle adjustment.
That will most likely lift your cheek off of the stock when aiming.
The TC factory scope mount is probably long out of production.
That's something to ask TC about, part numbers for the base and ring insert and availability.
Then you can begin searching using Google, on Gunbroker or on eBay to find a base and mount set for your Tree Hawk.