Shimano downtube shifters 3x7 speed
7 and 8 speed cassettes have the same spacing, so you can use either in your situation.

As for indexing on the rear, usually there is no indexing, though I've seen 'semi-indexing', where they do have an index mechanism, but it still requires several clicks to switch chainrings. 

Additionally, you sometimes need to adjust a little bit based on what gear you have selected in the rear. Spacing between chainrings can vary somewhat on different cranksets, it's not as rigidly specified as it is for the rear. 

The 3x7 shifters your LBS should work just fine.