Almost always SJS or Spa, with a little bit of
Wiggle and Planet X in the mix. I'm not in the market for components atm but I have used Fresh Tripe and BLB for stuff like Velo Orange (but nowadays, I might try harder to source a cheaper alternative). A few years ago and Rose would have been up there with SJS and Spa.
I've used some of the other larger chains, occasionally
Ebay, and some of the smaller outfits (like Parkers of Bolton) when the right product has been at the right price, but this is very rare. To be honest, I try to buy as little as possible.
Both my bikes (Jamis tourer and Tern folder) were sale items from
Evans and around the time I bought them (mid last decade), I did use Evans quite a lot but nowadays they hold almost zero interest to me - an uninspiring product line and never the right product at the right price.