Check out POSTFIX on Amazon. Quite a big range.

regards

I drove hardwood filler pieces into the the arris rail slots on my concrete fence posts and screwed ordinary galvanised folded sheet metal arris rail supports made for wood posts onto the filler pieces. Cheap from my local fencing contractor.

The alignment was sufficiently close to original that I could deal with individual posts as required. Ended up doing a 20 panel fence in 4 or 5 goes.

Not a good idea to drill concrete fence posts. Many are heavy on pebbles in the mix making getting a straight hole in the right place chancy. If you hit a pebble just so its likely to spall out taking a lump of concrete with it making a right mess. I've seen a post snapped by such spalling when a jobbing builder friend insisted that his monster hammer drill would go through just fine despite my doubts. The guy who put my fence in explicitly said not to try drilling the posts as bad things would happen. Those posts have been in nearly 50 years and still stand straight. I figure he knew what he was talking about.

Clive