Too bad that Greenwoods gone, so below is how I now get by very well.
I recommend, purely on the basis of customer satisfaction, The Tap and Die Co of London. Excellent quality and service. I do sometimes use Tracey tools who are also good. Both of them for taps and dies, slotter and endmills.
I dont use insert cutters as having a large stock of HSS tools and the means to resharpen, is good enough. I use a QCTP holder with a wedge type clamp for my parting off blade.
Brazed carbide tools for cast iron.