I used to use Cutwel as first choice when I was working. Industrial supplier, but they will sell to anyone and will sell individual inserts. Very good service and reliable (Korean) carbide, with a wide range of chip breakers and coatings.

Other suppliers included Zoro and MSC Industrial Supply, both of which also supply outside industry. Also used to search Ebay for obsolete inserts to suit cutters we used but for which the manufacturers had ceased production.

For my home use I just go for the 10 packs of Chinese inserts from Ebay - typically under a tenner for a pack delivered. They do the job, seem to last and don't cost the earth.

I don't know what lathe you have, but a hobby-sized lathe found in most garages won't be that bothered about what grade of carbide or coating you use - you won't be able to push it's performance envelope far enough to tell the difference in most cases. I tend to use HSS or brazed carbide on the Super 7 & Chinese carbide inserts on the Warco at the moment.

Nigel B.