Ceramic Tile edges

I know a lot of people do this, but it is a bodge, plain and simple. Just remove the tiles before tiling.

Many bodgers use quadrant tiles for this, they are readily available. But you may not be able to match the thickness of your double tile layer to the exact radius of the quadrant.

Yes, perhaps two strips side by side :-)

No. You will find them for some ranges of tile at specialist places. Normally, though, they are for thicker tiles where the edges are more pronounced and often these are the more expensive tiles. Look for dado tiles.

e.g.

Here's another supplier

Bad idea. They look really crappy and spoil the appearance.

I reckon it's often easier to remove the old ones & start afresh.

I'm sure I've seen them as well. Yours must be a common situation? Topps seem to have soething but not many details

IME of Topps, they don't stock any of the things like tile edge pieces (except the plastic strip ones), tile dado rail pieces, etc. They have to be ordered in specially, even though they are on the display panels. Also, although the tiles themselves can be good value, beware that all the other stuff (adhesive, edging, etc) more than makes up for that, if you aren't careful.