If you can't find, get Sora R3030 for the left, same pull on the 5703/6703 FD. The R3000s are very decent shifters in their own right (though 9 speed). Another alternate is the 4703, I currently run 6703 on my tourer/audax/winter racing machine and the right side Tiagra 4700s are better than the 6700 for rear shifting, the front mechs are cheap and the right/rear STI can be used with 105 11 speed rear Ds which has a slightly bigger capacity and again cheaper than the 6703 GS.
If/when the 6703s go I'll be swapping for 4703, problem is that Shimano are likely stopping triple STis, Tiagra 10x3 is about the same money as Ultegra 11 speed if you can find them.
Luck hunting
If you can't find, get Sora R3030 for the left, same pull on the 5703/6703 FD. The R3000s are very decent shifters in their own right (though 9 speed). Another alternate is the 4703, I currently run 6703 on my tourer/audax/winter racing machine and the right side Tiagra 4700s are better than the 6700 for rear shifting, the front mechs are cheap and the right/rear STI can be used with 105 11 speed rear Ds which has a slightly bigger capacity and again cheaper than the 6703 GS.
If/when the 6703s go I'll be swapping for 4703, problem is that Shimano are likely stopping triple STis, Tiagra 10x3 is about the same money as Ultegra 11 speed if you can find them.
Luck hunting