I would like to install a muzzle brake on a 338 magnum. Where would be the best place to have this done?

I would not have a muzzle brake on a 338 WM. I know they kick like heck but it's not a 458. Find some other way to lessen the felt recoil. The new soft recoil pads are a good place to start.

When your almost deaf it's not good. I know.

I feel your pain. I bought a light-weight, short-barrelled, stainless Ruger in .338 mag with plastic stock about ten years ago. The recoil was measured at a very unfriendly 37-38 lb.s I could't hit much of anything on the range after the 5th or 6th shot. Practice was like taking a beating. I priced my recoil-reduction options and sold the gun. The guy that bought it was a craftsman. He did a trigger job, put on a custom glass-bedded walnut stock with a super nice recoil pad and swore by it's accuracy. Good on him!

No pun intended, I hear others concerns regarding hearing loss. But, I have a little different take on muzzle brakes. I've found that to hunt effecitvely their is no substitute for shooting practice. I have found I shoot so much more accurately and more often with a brake. I have two BOSS equipped Win. 70's and a Ti Rem. 700 eith a Gentry brake. I'm planning to put a Que brake on a 30'6. I like to use the brakes on the range for the practice and on the BOSS equipped guns replace them with a CR/compensator at the same setting to hunt. The aim point doesn't change. Sometimes with my BOSS equipped 7mm Mag and always with the Rem. with the Gentry brake (compensator is not an option here) I use ear protection to hunt. Saves my hearing and keeps my ears warm.