The JC-70 has a 30/42/52 crankset, therefore any front derailleur made for a road triple should work. Shimano numbers them and ones rated for triples end with '03' so 4603 is a Tiagra and you can still find NOS 105 derailleurs 6603. Both will work. A mountain front derailleur won't work because it's designed for smaller chainrings, usually 44 teeth; so the profile won't match the outer 52T that you have. So don't look at anything starting with an "M."