I just use ebay.

This is a link to someone doing straight stainless in 1 5/8" - Stainless exhaust

It's the same one I used for the straights and the silencer. Delivery was very quick (24hrs) and free.

For bends, I tend to use the search terms 'jetex' and 'mandrel'. You can get them in a range of 'degrees' of bend.

All available in mild steel too.

Once I've got mine a set up properly and happy with the sound level, I'll get some of the main joints 'tigged' and lose the clamps.

1972 4/4 4 seater, 1981 MGB GT
1984 Harley Davidson Electra Glide, 1990 Kawasaki ZX10